WILKINS, J.

The defendant, who had been paying child support pursuant to court orders based on judicial determinations of his paternity, learned from the results of court-ordered blood grouping tests (conducted more than nine years after the first determination of his paternity) that he was not the child's biological father. He wants his money back. We conclude that on this record he is not entitled to reimbursement.

In April, 1981, the Commonwealth filed a criminal complaint against the defendant in the Pittsfield District Court for nonsupport of a child born in June, 1980. See G.L.c. 273, § 15, as amended through St. 1977. c. 848, § 6. The defendant, represented by counsel, pleaded guilty, and, in May, 1981, a judge adjudicated him to be the father and subsequently ordered him to pay weekly support for the child through the court's probation office. Nothing in the record discloses when the defendant first learned of his right to seek blood grouping tests. The child has apparently been on public assistance at all relevant times, and all support payments have been made to the Commonwealth.

In March, 1988, after enactment of G.L.c. 209C, the civil paternity statute (see St. 1986, c. 310, § 16), the Department of Revenue (department), acting through its child support enforcement division and on behalf of the child's mother, commenced a civil action in the Pittsfield District Court to establish and enforce the defendant's obligation to support the child. In April, 1988, the defendant appeared in court, and a judge again adjudicated the defendant to be the father of the child and ordered that the defendant make current support payments of $50 a week and contribute $5 a week toward outstanding child support obligations.

In September, 1990, in circumstances not fully disclosed in the record, a judge suspended the support order, and the parties filed a stipulation for blood grouping and genetic marker tests. The test results excluded the defendant as the biological father of the child. A judge, therefore, permanently suspended the child support order. On December 11, 1990, the defendant filed a motion in the civil action for remittance of all amounts that he had paid for child support. On January 15, 1991, after a hearing at which no evidence was presented, a judge allowed the motion. We transferred to this court the department's appeal from the order allowing the motion.

Each side urges that equitable considerations require a decision in its favor. The defendant argues that he has been obliged to pay for the support of a child of whom he is not the father and that he, in fairness, is entitled to restitution. He contends in particular that, because the department has been unjustly enriched, it should return the amount of the support payments. He also argues that he is entitled to recover on a claim of money had and received. The fatal weakness in these equitably based claims is that the defendant made all the payments pursuant to court orders that he did not challenge by appeal, one order entered following his guilty plea and the other entered in a civil action in which he had an opportunity to challenge the allegation of his paternity. It is not enough to show that the orders for support were based on a "mutual" mistake of fact. The defendant must present a substantial basis for vacating those judicial orders.

The department asserts, in turn, that the defendant is equitably estopped from challenging his paternity. It contends that, in the criminal nonsupport proceeding, the defendant could have contested his paternity and could have sought tests that would have disproved his paternity. See Commonwealth v. Beausoleil, 397 Mass. 206, 222 (1986). Instead, the defendant pleaded guilty. Similarly, as the department points out, the defendant could have challenged his paternity in the civil nonsupport proceeding and could have immediately sought blood tests. He did not do so, and a judge again adjudicated him to be the child's father. It is unclear on this record, however, that the department has relied to its detriment on any explicit or implicit acknowledgment by the defendant of his paternity. Nor does the record show any detrimental reliance by the mother or the child, even assuming that the department may assert their rights. A case for equitable estoppel of the defendant, therefore, is not made on this record.

Principles of issue preclusion, however, bar the defendant from contesting his paternity as to past support payments because his paternity was necessarily determined in the civil nonsupport action. See Anderson v. Anderson, 407 Mass. 251, 255 (1990); Fidler v. E.M. Parker Co., 394 Mass. 534, 539 (1985); Olsen v. Olsen, 294 Mass. 507, 509 (1936); Restatement (Second) of Judgments § 27 (1982). The issue of his paternity was raised and decided in that proceeding. The record is uninformative as to details of the hearing in the civil proceeding. We accept the representation in the defendant's brief that he appeared in court on April 26, 1988, and was adjudicated the father of the child.

In any event, the defendant presents no basis for retroactive relief from the child support order. Although we shall assume that the defendant could be relieved from the prospective application of the support order under Mass. R. Civ. P. 60 (b) (5), 365 Mass. 828 (1974), rule 60 (b) presents no basis for retroactive relief from the support order. Because what we have said is dispositive of the defendant's claim for retroactive relief from the support orders, we need not decide whether the prohibition against any "retroactive modification" of a child support order stated in G.L.c. 119A, § 13 ( a), inserted by St. 1987, c. 714, § 1, applies in the circumstances.

The order allowing the defendant's motion to remit, in effect directing the department to refund all child support payments that the defendant has made, is vacated. An order shall be entered denying the defendant's motion for remittance.

So ordered.