Dr. Terrazas cried on the telephone as he recounted the fallout. Because of the resulting dispute over child support payments, he said, he no longer sees his child regularly. His ex-wife's current husband is in the process of adopting the child.

He said that his relationship with the child "has been destroyed."

Dr. Terrazas's former wife answered a request for an interview with an e-mail message that said, "I do not want anything to do with any media coverage that focuses adversely" on her children. It is the fallout faced by the children, most child advocates and lawyers say, that is most traumatic. And the men who seek to halt child support payments -- an act many of them say is an attempt to right a wrong, rather than to abandon the children they still care about -- are surprised to learn that they are still required by many courts to continue to pay because it is deemed in the best interest of the child, especially if the man is the only father that child has ever known.

Some men have organized groups like the United States Citizens Against Paternity Fraud (www.paternityfraud.com) to call for mandatory DNA testing at the time of birth and laws that exempt men from child support if they are proven not to be the biological father.

"It's really a lose-lose situation," Debbie Kline, executive director of the Association for Children for Enforcement of Support, a child support advocacy organization, said of the situations when parentage isn't determined until long after birth. "And for the children, if this man is removed from the child's life, it's going to be devastating."

To prevent grief down the line, Mr. Leving said he recommends that his clients get a DNA test if they have a child out of wedlock. Other lawyers say men should think about the test even within a marriage if there's suspicion of an affair or any circumstance that does not pass "the smell test."

"I think the real bottom line is that for a few hundred dollars you can buy peace of mind that the child is yours," said Randall M. Kessler, a family law lawyer in Atlanta. Still, most men resort to DNA testing only when they are pushed. Lawyers like Mr. Leving say clients often request the test when they are being denied visitation rights and become suspicious of the reasons. In other instances friends or relatives -- and often a current girlfriend or wife -- might raise suspicion that a child is not theirs, or the mother herself might blurt it out.