Sixteen months after his divorce, Richard Parker made a devastating discovery. A DNA test revealed that his 3-year-old son had been fathered by someone else.

Mr. Parker immediately filed a lawsuit claiming fraud by his apparently unfaithful ex-wife. He took his case all the way to the Florida Supreme Court.

Last week, the Florida justices ruled 7-0 against him. They said that Parker must continue to pay $1,200 a month in child support because he had missed the one-year postdivorce deadline for filing his lawsuit. His court-ordered payments would total more than $200,000 over 15 years to support another man's child.

"We find that the balance of policy considerations favors protecting the best interests of the child over protecting the interests of one parent defrauded by the other parent in the midst of a divorce proceeding," writes Justice Kenneth Bell for the court.

"We recognize that the former husband in this case may feel victimized," he writes. He then quotes a scholar to explain the ruling: "While some individuals are innocent victims of deceptive partners, adults are aware of the high incidence of infidelity and only they, not the children, are able to act to ensure that the biological ties they may deem essential are present."

In effect, the high court is saying it's partly Parker's fault for trusting his wife.

The Parker case illustrates an increasingly contentious debate over the rights and responsibilities of divorced fathers who have been duped and don't challenge paternity at or near the time of divorce. But it also raises fundamental questions about the nature of fatherhood and the legal responsibilities that can attach to a father-child relationship – even when that relationship is the result of fraud and deception by a wife and mother.

Most states have laws that permit courts to order men who have been deceived to continue to make child- support payments even when they have no biological connection to the child. The idea is to minimize any disruption in the life of the child. In recent years, some states have begun passing laws that give deceived dads some ways to fight back.

There are no reliable estimates of how often "paternity fraud" takes place. Some findings suggest 4 to 10 percent of fathers, but no definitive study has been completed.

Unlike most duped ex-husbands in the US, Parker may still prevail in court. Last summer the Florida legislature passed a law that allows men to use newly discovered paternity evidence (like Parker's DNA test results) to overturn a court order to pay child support for someone else's child.

The June 2006 law is aimed at preventing the kind of outcome ordered by the Florida Supreme Court. The policy approach taken by the Florida Legislature stands in sharp contrast to the "policy considerations" cited by the state supreme court justices.

Supporters of the Florida law see it as a major step toward justice for deceived ex-husbands. Critics see it as a potential danger to the well-being of mothers and their vulnerable children.

In addition to Florida, Ohio, Georgia, Maryland, Alabama, Indiana, Virginia, Arizona, and Wyoming have laws allowing ex-husbands to overturn a child-support order when deception or fraud by an ex-wife is discovered, according to the National Conference of State Legislatures. By contrast, most other states set a one- to four-year deadline for fathers to file lawsuits challenging paternity determinations.

The idea behind the deadline is that any action taken in a marriage breakup should be completed while the child is as young as possible to avoid a major disruption during the most formative years.

"We don't want a system where a child is 10 years old and you have people who come in and undo what has been put in place many years before," says Susan Paikin of the Center for the Support of Families in Silver Spring, Md.

Ms. Paikin says that it is up to the adults in the relationship to thoroughly investigate any paternity issues at the time of the divorce.

But fathers' rights advocates say that few husbands are aware of a paternity deadline and its legal implications. And many have no idea that their wives have been unfaithful.

In generations past such infidelity might have gone undetected. But the advent of DNA testing is changing that. It is giving new momentum to a debate over how best to provide for broken families.

"There is no perfect answer," says Paikin. "There are a lot of people who will argue that it is always in the child's best interest to have a relationship with the biological parent and that should override everything else. There are others who believe just as fervently that being a parent has more to do with being caring and nurturing, and that is what makes you a father."

Part of the difficulty in paternity disestablishment cases is that once the financial contribution of the nonbiological father is terminated, the courts do not recognize a legal right to continued contact between the child and the man.

"It is the ultimate Catch-22 for my client," says Parker's lawyer, Scott Lazar of Miami. "On the one hand he has a relationship with this child and cares about this child and would probably be willing to provide money for this child, but he doesn't want to provide it to the mother to use as she wishes."

Family court judges aren't interested in fostering a continuing relationship between men and the children of their ex-wives, says Carnell Smith, who runs a DNA-testing company and is founder of Atlanta-based US Citizens Against Paternity Fraud. "The court is only concerned about financial payments."

Judges generally view the man in a divorce proceeding as nothing more than a "walking checkbook," he says.

Smith says that instead of targeting deceived ex-husbands, the legal system should investigate the conduct of the wife and hold the mother and biological father responsible for the child they produced.

"In no other area of the law do we punish the victim for the conduct of two other people," Smith says. "For me it is disingenuous for the Florida justices to turn around and say [to Parker] 'Well, it is your fault that you didn't find out sooner.' "

The Florida legislature tried to balance the law to avoid forcing children onto welfare rolls, says Tom Sasser, chairman of the family-law section of the Florida Bar. It rejected a proposal to allow ex-husbands to recover prior child-support payments. It also rejected a proposal to allow triple damages against deceptive mothers. Instead, the law allows ex-husbands to be released from future payments.

And that, advocates say, opens the door for some ex-husbands to attempt to build a trusting relationship with someone new and perhaps start a family without the burden of a court-imposed financial debt hanging over his new wife and children.