The Supreme Court of Missouri on Tuesday rejected the University of Missouri System's appeal in a class-action lawsuit alleging that the system violated state law for 15 years by charging tuition to in-state undergraduates. The university could face a judgment amounting to hundreds of millions of dollars.

The case will now return to the state court for St. Louis County, where Judge Kenneth M. Romines ruled last December that the university system's four branches -- at Columbia, Kansas City, Rolla, and St. Louis -- had illegally charged students the equivalent of tuition by collecting "educational fees" to defray expenses not covered by state appropriations.

Under a 19th-century statute, the state was prohibited from charging tuition to qualified Missouri undergraduates over the age of 16. The court ruled the illegal activity took place from 1986 to 2001, the period between when the system introduced its first per-credit-hour charge and when the state General Assembly revised the law.

"We're assuming the Supreme Court will send it back to the trial court to determine a remedy and damages, if any," said David R. Russell, the system's director of university relations, who said he had not yet received details of the court's decision. The court remanded the case without comment.

Taking into account the statute of limitations, damages may be extended to all in-state University of Missouri students -- up to 150,000 -- since 1993. The sum may take the form of monetary relief, or education vouchers for continuing study or for use by plaintiffs' children. If the judge orders full reimbursement of all educational fees from 1993 to 2001, the university system may be forced to pay up to $450-million in damages, plus interest.

The university system lost its appeal because it filed the appeal too early, said Robert Herman, a lawyer representing the plaintiffs. In the original trial, he explained, the liability and remedy portions were split. The system filed its appeal immediately after the liability phase and before the trial court had ruled on a remedy, a step that is considered a legal mistake.

"I'm glad the Supreme Court is treating this case like any other," Mr. Herman said, "and does not dismiss a case before it's complete."