delivered the Opinion of the Court.
Thе parties, Lawrence and Jean Cooper, obtained a dissolution of marriage in the District Court, Thirteenth Judicial District, Gallatin Cоunty, on August 19, 1975, after 29 years of marriage. Three children were born and raised by the parties. They were all emancipated at the time of the dissolution. The parties entered into a property settlement agreement which was incorporated into аnd made a part of the 1975 decree of dissolution. Included in this agreement was a provision relating to maintenance which provided that Lawrence Cooper pay $4,200 in seven equal installments of $600 to his former wife. The decree further provided that аt the termination *36 of said installments, if the parties hereto are unable to agree upon the amount of alimony to be pаid to the wife, if any, the wife reserves the right to present this matter to the court having jurisdiction for a determination of the amount of mоney to which she would be entitled for alimony.
Lawrence Cooper paid the $4,200 pursuant to the above provision. In August, 1976, Mrs. Cooper filed a petition requesting a determination of alimony pursuant to the provision in the original decree. After a hearing on November 22, 1976, the District Court issued an order denying Mrs. Cooper any maintenance. The order was not appealed.
On Novembеr 17, 1982, nearly six years later, Mrs. Cooper (hereinafter respondent), filed a petition requesting modification of the original divorсe decree and requesting that Mr. Cooper (hereinafter appellant), pay respondent the sum of $1,500 per month for her maintenance. Appellant moved to dismiss respondent’s petition on the grounds that it was barred by res judicata. The District Court deniеd appellant’s motion and set a hearing for May 24, 1983, to consider evidence of changed circumstances. Appellant and respondent were both present and testified at the hearing. On October 25, 1984, the District Court entered findings of fact, conclusions of law, and an order requiring appellant to pay the sum of $750 per month to respondent for her support. It is from this order that appellant appeals.
Appellant contends that the respondent’s petition is barred by the doctrine of res judicatа. Basically, res judicata applies when a court of competent jurisdiction renders a final judgment on the merits. The judgment is cоnclusive and binding on the parties and their privies in all later suits on all matters determined in the former suit. The general principle of rеs judicata has been altered by statute in Montana for cases involving the dissolution of marriage. Section 40-4-208, MCA, governs the modification of maintenance and property disposition provisions contained in the dissolution decree. We must interpret this statutе to determine whether under the facts of this case the decree may be modified to award respondent maintenancе. Section 40-4-208, MCA, provides in pertinent part:
“40-4-208. Modification and termination of provisions for maintenance, support, and prоperty disposition. (1) Except as otherwise provided in 40-4-201(6), a decree may be modified by a court as to maintenance or support only as to installments accruing subsequent to the motion for modification.
*37 “(2) (a) Whenever the decree propоsed for modification does not contain provisions relating to maintenance or support, modification under subsectiоn (1) may only be made within 2 years of the date of the decree.
“(b) Whenever the decree proposed for modification contains provisions relating to maintenance or support, modification under subsection (1) may only be made:
“(i) upon a showing of changed circumstances so substantial and continuing as to make the terms unconscionable; or
“(ii) upon written consent of the parties.”
A petition for modificаtion with respect to maintenance must be considered by the District Court if it is filed within two years of the date the decree is rendered, regardless of whether the decree contains provisions for maintenance or whether maintenance payments аre currently being paid. If two years has expired since the dissolution decree was rendered, modification is still possible when the decree contains a provision relating to maintenance. When maintenance payments are currently mandated under the decree, a modification petition must be considered by the District Court. We recently stated in
Rush v. Rush
(Mont. 1985) [
Respondent contends that the same rule should apply in the instant case. She argues that since the original decree containеd a maintenance provision, the District Court was correct in entertaining her petition for modification. We disagree. In this cаse the decree in force in 1982 was the decree as modified by the 1976 order of the District Court. In the 1976 order, the court ruled the respondent was not entitled to any maintenance. The effect of this order was to *38 delete the maintenance provision from the decree. Hence, the decree prоposed for modification by respondent did not contain a provision for maintenance and could only be modified befоre November 22, 1978.
Since we hold that respondent’s petition for modification is barred by Section 40-4-208(2)(a), MCA, we do not reach the rеmaining issues presented by appellant. The judgment of the District Court is reversed and the order granting respondent maintenance is vacated.