For American parents looking for donor sperm to produce blond, blue-eyed Scandinavian babies, the search just got a little trickier.

A ban on sperm from all European countries with exposure to mad cow disease means U.S. sperm banks are running low.

The May 2005 decision by the Food and Drug Administration effectively blocked donors from Denmark to the United Kingdom. And while some sperm banks have had enough frozen stocks to cope with demand, they are now facing shortages.

"We still have a little bit left, but not much," said Claus Rodgaard, manager of Cryos International, a Danish-based sperm bank with an office in New York.

"We're not here to promote people to have blond, blue-eyed babies, but if those are the kinds of characteristics you're looking for, then Danish sperm is good for that," Rodgaard said. "That's all we have in Denmark."

Scientists say the ban is not justified.

"The consensus in the United Kingdom is that this is a silly ban," said Dr. Allan Pacey, an andrology expert at the University of Sheffield and secretary of the British Fertility Society. "There's no evidence to show that mad cow disease can be transmitted in human semen."

The human form of mad cow disease, variant Creutzfeldt-Jakob disease, is mainly transmitted after people eat infected meat. In rare cases, the disease has been spread by contaminated surgical equipment or in transplants of brain tissue. There has never been a documented case of variant Creutzfeldt-Jakob being passed on after a sperm donation.

Pacey said concerned doctors could always screen potential donors to see if they might be at high-risk for mad cow disease, but that a blanket ban was unnecessary.

Dr. Gianpiero Palermo, an associate professor at Cornell University's Center for Reproductive Medicine, agreed. "I'd be more worried about genetic diseases," he said.

Diseases including HIV/AIDS, hepatitis, or bacterial infections like chlamydia would be far more likely to be spread by sperm donors, doctors said.

Rodgaard said the FDA has been asked to reconsider the ban, but there has been no sign it will be lifted soon. "It's a completely random decision," he said, pointing out that even though Canada has reported mad cow cases, "you are still allowed to import all the tissue you want from Canada."

For the moment, the best option for American parents desiring children of European stock may be to travel to Europe. "We just have not been able to import any more Scandinavian sperm," Rodgaard said.

Palermo said the ban has not had a big impact.

"There's absolutely no difference between American and European sperm," he said. "If you are looking for a specific type of donor, we can find whatever genetic qualities you want in the U.S."