MEMORANDUM AND ORDER
The plaintiff, Roger W. Giese, commenced suit against the defendants, Vector Laboratories, Inc. (“Vector”) and Pierce Chemical Co. (“Pierce”), alleging contributory infringement and inducement of infringement of Giese’s patents, United States Letters Patent Nos. Re.31,712 (“the ’712 Patent”) and Bl,4,478,-914 (“the ’914 Patent”).
The patents cover a method by which multiple layers of chemicals are attached to one another to form a stable system. The resulting system typically is used to improve detection of certain types of cells, for example, cancer cells. Vector manufactures a kit of chemical reagents marketed under the trade name “Vectastain ABC Kit”, a product designed to assist in the marking and detection of various tyрes of cells. Pierce purchases' the kits for subsequent resale. Giese maintains in his Amended Complaint that the ABC Kits “incorporate the technology dis *35 covered by the Plaintiff.” Amended Complaint ¶ 9. Giese further alleges that the defendants use “a component of Dr. Giese’s patented technology in its ABC Staining Kits which component constitutes a material part of Dr. Giese’s invention.” Amended Complaint ¶ 15. On the strength of these allegations, Giese contends that both Vector and Pierce have contributed to or have actively induced the direct infringement of the patents. Giese includes no count for direct infringement.
Vector and Pierce come now before this Court with three separate motions for summary judgment. The first seeks pаrtial summary judgment on the ground of non-infringement as to certain end users of the kits. The second is based on the doctrine of laches. The third asserts equitable estoppel. For the sake of clarity, this memorandum will address each motion separately.
I. NON-INFRINGEMENT
The defendants’ first motion for summary judgment asserts non-infringement under the common law experimental use exception to patent infringement.
See Roche Prods., Inc. v. Bolar Pharmaceutical Co.,
A. Facts
The facts underlying this motion are undisputed, but not well developed. The parties agree that a substantial portion of the ABC kits are sold to academic researchers, but there is no agreement on exactly what proportion, and no information at all as to which users fall into that category. 1 It is also undisputed that the sales literature states that the kits are designed to be used for research purposes only.
Further, Vector concedes that some of its sales are to commercial users, and does not seek summary judgment as to those users. Vector also concedes that it sells kits to Pierce, which then resells them. As to those kits, Vector argues that Pierce does not practice the patented methods, and that any infringement must be based on infringement by end users who do practice the patented methods without permission. Vector, invoking the same syllogism it applies to its own direct sales to consumers, argues that only commercial users purchasing from Pierce may infringe.
B. Analysis
The experimental use exception to the patent infringement provisions of 35 U.S.C. § 271 has its origins in the notion that “it could never have been the intention of the legislature to punish a man, who constructed ... a [patented] machine merely for philosophical experiments .... ”
Whittemore v. Cutter,
Roche established a restrictive definition of the traditional common law doctrine, but in no way eliminated it in those cases which involve experimentation for “idle curiosity or for strictly philosophical inquiry.” Id. Giese does not dispute that the doctrine applies in some instances, yet because the record contains no information about the actual experimental use, this Court need not and cannot decide at this point whether any particular use falls within the exception.
Giese, however, challenges the application of the doctrine on a different ground: that Vector and Pierce profit from the sales of the kits, regardless of whether they are put to use for experimental purposes or for purely commercial purposes. That profit, asserts Giese, deprives Giese of a benefit which derives from the use of his patented processes, and thus should deprive the defendants of the shelter of the experimental use exception.
Giese’s analysis is flawed, and would allow him to protect rights beyond those conferred upon him by the patents. Both the ’712 and the ’914 patents are method patents. Infringement of a method patent consists of practicing the claimed methods; the materials used to practice the methods are not themselves protected. In order to prevail on a direct infringement claim, Giese wоuld need to prove either that the kit is manufactured using the claimed methods, or that he owns a patent covering the material composition of the reagents in the kit. Giese makes no such claims. Indeed, his claims are directed at contributory infringement and inducement, theories based on the encouragement or facilitation of direct infringement by others.
Giese’s claims in this case therefore must be grounded on allegations of direct infringement by the end-users of the kits. Customers allegedly purchase the kits in order to practice the protected methods because the kits are specially adapted or made for such use.
See
35 U.S.C. § 271.
2
The only actions of the defendants that could be deemed infringing under these theories are the sales of the kits to infringers. Liability depends, however, upon the direct infringement by third parties. Absent direct infringement, there can be no inducement or contributory infringement.
See Joy Technologies, Inc. v. Flakt, Inc.,
If the end users are not infringers due to the protection of the experimental use doctrine, then the defendants Vector and Pierce cannot be liable for contributory infringement or inducement. It makes no difference that Vector and Pierce benefit financially by selling the kits because they are selling kits to end-users who have the right to practice the patented methods.
Cf. Met-Coil
Having reached that legal conclusion, however, the Court is without the necessary showing to grant summary judgment. Vector and Pierce have made no showing that the end-users, or any of them, fall within the exemption. Although Giese has not made a contrary showing, it is the burden of the moving party to establish the absence of genuine issues of material fact, see Fed. R.Civ.P. 56, and the defendants have not done so. As a result, the motion for summary judgment of non-infringement is DENIED.
II. LACHES
The second motion for summary judgment asserts the equitable defense of laches. Vector and Pierce argue that Giese’s delay in asserting his rights under the patents, despite having knowledge of Vector’s product for many years, renders it inequitable to allow him to claim damages from the alleged infringement at this late date. Giese asserts that there are various events during the relevant period that should be regarded as excusing his delay.
A. Facts
The following chronology of relevant events is established by the record.
1.The Patents
U.S. Patent No. 4,282,287 was issued to Giese on August 4, 1981. Upon Vector’s suggestion that the patent might be anticipated by prior art, Giese applied for reissuance on May 3, 1982, and again on September 14, 1983. The ’827 patent was reissued on Octоber 23, 1984, over the formal protest of Vector, 3 as U.S. Patent No. Re. 31,712, one of the patents now in suit.
A continuation of the ’287 patent, U.S. Patent No. 4,478,914, was also issued on October 23, 1984. The ’914 patent was later subject to reexamination following the suggestion of a third party that there may have been another prior art reference; the Reexamination Certificate issued under No. B1 4,478,914 on June 17, 1997. The ’914 patent is also one of the patents now in suit.
2. The Parties
On August 11, 1981, Giese’s counsel wrote to Vector’s president to notify Vector that its ABC kits might infringe on Giese’s (then) ’287 patent. An exchange of correspondence followed between the two principals and their counsel, to the effect that Giese offered a licensing agreement, but that Veсtor denied infringement and suggested the anticipation of the patent by prior art. That exchange concluded on December 21, 1981.
On July 7, 1982, Giese advised Vector through counsel that a reissue application had been filed, and invited Vector to participate in the proceedings. Vector did file a formal protest with the Patent and Trademark Office.
The next direct communication between the parties occurred on December 31, 1991, when Giese again informed Vector through counsel that he considered Vector’s products potentially infringing, and again invited negotiations concerning a licensing agreement. On January 14, 1992, Vector responded that it was reviewing the patents and its products. Vector nеver notified Giese of the results of that review. 4 On July 18, 1997, Giese invited Vector to discuss a license of the now reexamined ’914 patent. Vector replied again that its kits did not infringe on the patent. At no time did Vector identify to Giese any prejudice it had suffered as a result of Giese’s delay.
3. The Licensing Agreements
As a result of the reissue proceeding, Giese was without resources to pursue poten *38 tial infringers between May 1982 and October 1984. On April 25, 1985, Giese entered into an exclusive licensing agreement with Beckman Instruments, Inc. During the term of the agreement, Beckman had the sole right to bring actions for the enforcement of the patents. That agreement terminated in February 1991. Between 1991 and 1992, Giese approached a number of other companies to explore licensing arrangements, and engaged in negotiations with several. Giese ultimately entered into an agreement with Boehringer Mannheim for a non-exclusive license in October 1994.
B. Analysis
1. Applicable Law
Unreasonable and inexcusable delay in filing suit to enforce a patent that causes material prejudice to the alleged infringer gives rise to a defense of laches.
See A.C. Aukerman Co. v. R.L. Chaides Const. Co.,
Application of the defense of laches must be flexible, and depends on all of the circumstances of the particular case and the equities involved. The Federal Circuit, however, has articulated a set of factors that the defendant invoking laches must prove: First, that “the plaintiff delayed filing suit for an unreasonable and inexcusable length of time from the time the plaintiff knew or reasonably should have known of its claim against the defendant.” Second, that “the delay operated to the prejudice or injury of the defendant.”
Aukerman,
Prejudice to the dеfendant may be either economic or evidentiary. Economic prejudice consists of damages or the loss of monetary investments which likely would have been prevented by earlier suit.
See id.
at 1033. Ordinarily, such prejudice results from a change in the position of the defendant during the period of delay.
See Lake Caryonah Improvement Assn. v. Pulte Home Corp.,
A court must also consider any justification offered by the plaintiff for its delay. Among the excuses that have been recognized in some instances are: other litigation, negotiations with the accused, poverty and illness under limited circumstances, war, minimal infringement, egregious behavior by the accused, and dispute over ownership of the patent. See id. and cases there cited.
There is no statute of limitations in patent infringement actions, but there is a six-year damage limitation period. 35 U.S.C. § 286 (damages limited to infringement during the six year’ period preceding the filing of suit). Courts have borrowed this period to serve as the period giving rise to a rebuttable presumption of laches. If a patent holder delays more than six years in bringing suit after learning of the infringement, the presumption creates a prima facie defense of laches.
See id.
at 1034-37. The period may not begin, however, before the issuance of the patent.
See id.
at 1032;
Watkins v. Northwestern Ohio Tractor Pullers Assn., Inc.,
The presumption operates to establish the elements of unreasonableness and prejudice,
*39
absent rebuttal.
See Aukerman,
2. Giese’s Delay Gives Rise to the Presumption
Giese filed this action on November 17, 1997. It is undisputed that Giese knew of Vector’s potential infringement on the original ’287 patent by August 11, 1981, when he so informed Vector through counsel. But the ’712 and ’914 patents on which Giese bases his claims were not issued until October 24,1984. Thus, the period of laches with respect to Vector began on October 24, 1984.
Vector entered into its agreement with Pierce on May 23, 1989. Giese’s claim аgainst Pierce arose no earlier than that date, because there is no indication that Pierce sold ABC kits before entering into the agreement. Thus, the period of laches with respect to Pierce began on May 23, 1989.
Both parties have therefore established that Giese delayed more than six years after learning of their potential infringement before filing suit. The burden thus shifts to Giese to produce evidence that its delay was reasonable or excusable, or that Vector and Pierce were not thereby prejudiced.
3. Rebuttal
a. Prejudice
Giese introduces no evidence on the subject of prejudice, either to show that evidence of Vector’s and Pierce’s defenses remains available substantially as beforе the delay, or that Vector and Pierce have not suffered economic prejudice. Giese does question the validity and credibility of the defendants’ assertions of prejudice, but nothing in the record supplies the “minimum quantum of evidence” necessary to burst the presumption.
Aukerman,
Giеse merely points to weaknesses in the defendants’ affirmative proof. “Such an attack is, of course, unavailing, inasmuch as the defendants could have remained utterly mute on the issue of prejudice and nonetheless prevailed.”
Hall v. Aqua Queen Mfg., Inc.,
b. Unreasonable Delay
Giese does, however, come forward with evidence pertaining to the reasonableness of his delay. Giese advances three factors in support of his position: 1) other litigation concerning the patents before the Patent and Trademark Office; 2) licensing negоtiations with the defendants and others; and 3) reex- *40 animation of the ’914 patent. The court must determine whether any of these factors are legally cognizable excuses for Giese’s delay, and if so whether they are properly supported in the record.
i. Other Litigation
First, Giese argues that his delay is excused by the reissue and reexamination proceedings because those proceedings constitute “other litigation” in the sense recognized in
Aukerman. See Vaupel Textilmaschinen KG v. Meccanica Euro Italia SPA,
The reissue proceedings spanned the period from May 3,1982 to October 23,1984; the reexamination proceedings spanned the period from May 1995 to June 17, 1997. As to the first of those periods, this memorandum has concluded that laches did not begin to run until the October 1984 reissuance. The pre-1984 period is therefore irrelevant. As to the 1995-1997 proceedings, whatever tolling effect they may have began over ten years into the laches period. Even if the reexamination proceedings provide a legally cognizable excuse for the two years during which they were pending, they have no bearing on the preceding decade of delay. Thus, even though Giese comes forward with affirmative evidence, that evidence does not materially disturb the presumption of unreasonable delay.
ii. Negotiations
Giese next contends that the period of delay from 1991 until 1994 is excusable on the basis of negotiations between Giese and a number of other companies concerning the possibility of licensing his technology. The reason for such tolling is that a plaintiff’s continuous and bilaterally progressing efforts to resolve the patent dispute justify delay in bringing suit. See
General Elec. Co. v. Sciaky Bros.,
Giese contends that the Court must consider negotiations with all other parties, in addition to the defendants, in considering this rebuttal evidenсe. Giese cites
Meyers v.
As
ics Corp.,
Moreover, such treatment is inconsistent with the rationale behind the rule. The fact that Giese was negotiating with Boehringer Mannheim for the non-exclusive licensing of his technology has no bearing on his dispute with Vector and Pierce over their potential infringement. Nor does it alter the equities involved in Giese’s delay in bringing this suit. Third party negotiations simply do not represent an attempt to resolve the dispute with the defendants short of litigation— the main justification for tolling during negotiations. A comparison of the negotiation justification with the litigation justification is instructive. “Courts have generally held that a patentee need not sue more than one infringer at a given time. Any delay due to
*41
involvement in other litigation is considered excusable and hence not chargeable to the patentee as unreasonable delay.”
Watkins v. Northwestern, Ohio Tractor Pullers Assn., Inc.,
Giese does not argue that it was conducting negotiations with Vector during the relevant period. Indeed, the record reflects a series of rebuffed offers to negotiate. Vector consistently denied infringement over the course of the parties’ sporadic contacts, and nothing in the record indicates any bilateral negotiation or progress toward settling the dispute.
iii. Awaiting Related Patent
Third, Giese argues that he was not required to file suit for infringement of the ’712 patent before the reexamination of the ’914 patent was complete, citing
Meyers v. Brooks Shoe, Inc.,
This case is distinguishable from
Meyers
in at least two material respects. In this case, both patents had been issued for years when the reexamination application wаs filed. Giese does not suggest that he could not have sued on the ’914 patent before its reexamination, nor does he provide any authority so holding. In contrast, the patent holder in
Meyers
was constrained to wait on the later issued patent because he had no rights to enforce it prior to issuance. For related reasons, the parties in
Meyers
occupied a different position with respect to the laches presumption. Not only had the plaintiff in
Meyers
delayed for less than six years, but the period of laches cannot begin until the issuance of the patent.
See Aukerman,
In reaching the conclusion that there is no triable issue of fact as to the reasonableness of Giese’s delay, the Court relies on a particular understanding of the laches presumption that bears explicit articulation. Stated plainly, this understanding is that evidence of reasonable excuse for delay is not material, even if otherwise legally cognizable, if a continuous six year period of delay remains unexplained. The alternative understanding would be that legally cognizable evidence of reasonable excuse would always eliminate the presumption, regardless of the period of unexplained delay remaining. Although no court has addressed this specific problem, the former view is more persuasive. An excuse that leaves a presumptively unreasonable period of delay unaccounted for does not create a genuine issue of material fact as to the reasonableness of the entire delay. The Court therefore concludes that evidence of the reexamination of the ’914 patent does not create a genuine basis for disputing that Giese’s delay in bringing suit was unreasonable.
iv. Other excuses
In passing, and without argument, Giese alsо states that he was at various times .without resources to pursue legal action against Vector and Pierce, or that he was contractually precluded from doing so. Neither matter has been recognized as a legal excuse for delay.
See Leggett v. Standard Oil Co.,
149
*42
U.S. 287, 294,
Because Giese has not offered evidence sufficient to create a genuine issue of material fact as to the reasonableness of its delay or the prejudice to the defendants, he has failed to dissipate the presumption. The Court is therefore required to infer from the six year delay both unreasonableness and prejudice to the dеfendants.
4. Inequitable Conduct of Defendant
Giese offers no evidence or argument that Vector or Pierce have engaged in misdeeds that would alter the balance of the equities. An example of such behavior is intentional infringement or conscious copying of the patented process, whereas a good faith belief in non-infringement would tilt the equities toward the defense.
See Aukernian,
5. Equitable Discretion
The establishment of the presumption of laches does not end the inquiry. “With its origins in equity, a determination of laches is not made upon the application of ‘mechanical rules.’ ”
Aukerman,
Considering the unexplained delay of over ten years, the repeated charges of infringement and repeatedly rejected licen-sure overtures, and the absence of any demonstrated culpable behavior by the defendants, this Court concludes that Vector and Pierce have satisfied their burden of persuasion, and that Giese is barred by the doctrine of laches from bringing suit for damages incurrеd during the period of his delay. The motion for summary judgment of laches is therefore GRANTED.
III. EQUITABLE ESTOPPEL
The defendants’ third motion for summary judgment is based on the theory of equitable estoppel. This defense is closely related to laches, but differs in important respects. As a practical matter, estoppel may bar all relief, including injunctive relief, while laches only bars pre-filing damages. See
Aukerman
The first element, misleading communication, may be nothing more than misleading inaction. See id. at 1042. Such inaction, however, must be combined with “other facts respecting the relationship or contacts between he parties to five rise to the necessary inference that the claim against the defendant is abandoned.” Id.
The second element, reliance, is not an element of laches (although the prejudice element of laches may involve similar factual circumstances) yet it is essential to estoppel. Prejudice may bе shown without reliance, as where an infringer, unaware of the patent he is violating, builds a factory to manufacture a protected article. In this example, in order to show reliance, the defendant must show, in addition to prejudice, that he was lulled into building the factory by some aspect of the *43 relationship or communication with the patent holder. See id. at 1042-43.
The third element, material prejudice, is established with the same evidence used in the laches context, and may involve either economic or evidentiary prejudice. See id:
Most importantly, there is no presumption involved in the equitable estoppel context. The defendant must prove each element using competent evidence.
In this case, Vector and Pierce rely heavily on the laches presumрtion to establish then-estoppel defense. When put to their proof, however, they offer the following evidence of detrimental reliance. The defendants submit that there was a seven year period of complete silence between the parties between October 1984 and December 1991. That silence was broken by a letter informing Vector that its products appeared to infringe on the ’914, ’712, and a third related patent. In July 1995, Giese sued Vector for infringement of the third patent, but not for infringement of either the ’914 or the ’712 patent. Vector and Pierce argue that the failure to include the ’914 or the ’712 patents in the suit persuaded them that there was no further dispute with respect to those patents.
Giese presents the episode in a different light. Vector and Giese entered into a nonexclusive licensing agreement covering the third patent, as part of a settlement of the 1995 litigation. See Declaration of Giese ¶24, Ex. 9. That agreement specifically excludes the ’914 and ’712 patents from its coverage, and extends only to certain Vector products not involved in this suit. See id. The agreement further provides an admission that those particular products do not infringe any other patents Giese holds, “excepting only the Patent Rights that are the subject of this agreement and that such products may be used in such a manner so as to infringe such other patents.” Giese submits that this agreement indicates an explicit reservation of rights under the ’914 and ’712 patents, and a refusal to authorize Vector to practice the methods covered by those patents.
Giese would have the Court infer that Vector could not have relied on his behavior or representations to conclude that the ’914 and ’712 patents would not be enforced, because in the course of dealings his dealings with Vector he expressly reserved that option. Vector would have the Court infer that Giese acted to enforce patents when it chose to, and abandoned those patents it did not chose to enforce. It would be as permissible for the finder of fact to credit Giese’s inference, as it would be to credit Vector’s. Either inference is supportable on the reсord presented. In order for the Court to draw an unfavorable inference against Giese, however, the inference “must be the
only
possible inference from the evidence,”
Aukerman,
IV. CONCLUSION
The Court confronts three separate motions for partial summary judgment. On the first motion, for partial summary judgment of non-infringement, the Court concludes that sales of ABC kits for uses that are protected under the common law experimental use doctrine cannot constitute either contributory infringement or active inducement of infringement, because there is no direct infringement. Vector and Giese, however, have not succeeded in demonstrating the applicability of the experimental use exception to any particular customer or customers. Therefore, the motion of Vector and Giese for partial summary judgment of non-infringement is DENIED.
On the second motion, for summary judgment of laches, the Court concludes that Vector and Pierce have established at least a six year delay between Giese’s discovery of the alleged infringement and the filing of suit, thus giving rise to a presumption of laches. Furthermore, the Court concludes that Giese has failed to produce evidence sufficient to rebut that presumption, and therefore infers the elements of unreasonable delay and prejudice to the defendants. Based on those factоrs, the absence of inequitable conduct on the part of Vector and Pierce, and all the pertinent facts and equi *44 ties, the Court holds that Giese is barred from maintaining an action for the recovery of damages incurred during the period of his unreasonable delay. The motion of Vector and Pierce for summary judgment of laches is therefore GRANTED.
On the third motion, for summary judgment of equitable estoppel, the Court concludes that Giese has established the existence of a genuine issue of material fact as to the element of reliance. The motion of Vector and Pierce for summary judgment of equitable estoppel is therefore DENIED.
Notes
. A list of "some of the more well-known institutions” is appended to the Deсlaration of James S. Whitehead as Appendix B. The Appendix lists over one hundred institutions, but the record is devoid of evidence concerning each institution's use of the kits. At trial, it would be open to Giese to show that any or all of these institutions engage in direct infringement not protected under the common law exception.
. Section 271 provides in relevant part:
(a) Except as otherwise provided in this title, whoever without authority makes, uses, offers to sell, or sells any patented invention, within the United States or imports into the United States any patented invention during the term of the patent therefor, infringes the patent.
(b) Whoever actively induces infringement of a patent shall be liable as an infringer.
(c) Whoever offers to sell or sells within the United States or imports into thе United States a component of a patented machine, manufacture, combination or composition, or a material or apparatus for use in practicing a patented process, constituting a material part of the invention, knowing the same to be especially made or especially adapted for use in an infringement of such patent, and not a staple article or commodity of commerce suitable for substantial nonin-fringing use, shall be liable as a contributory infringer.
. Although Vector had notice of the first application, and participated in the proceedings, Giese did not notify Vector of the superceding application or of the reissuance.
. Vector did, however, enter into a licensing agreement covering another patent, U.S. Patent No. 4,656,252, in settlement of an infringement suit filed by Giese.