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

In May 2005, the U.S. Food and Drug Administration decided to ban sperm from any European countries with exposure to mad cow disease, effectively striking off donors from Denmark to the United Kingdom. While some sperm banks have had enough frozen stocks to cope with the demand, they are now running low.

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

Pacey said that 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.

Other experts agreed the possibility of sperm transmitting mad cow disease was negligible. "I'd be more worried about genetic diseases," said Dr. Gianpiero Palermo, an associate professor at Cornell University's Center for Reproductive Medicine.

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 that the FDA has been asked to reconsider their decision, but that they have not had any signs that the ban might soon be lifted. "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.''

Canada does not ban the importation of semen from any country, but any semen imported into Canada is strictly regulated under the Food and Drugs Act and the Assisted Human Reproduction Act, Carole Saindon, a spokesman for Health Canada, told The Canadian Press in an e-mail.

"The Semen Regulations, under the Food and Drugs Act, specify strict requirements for the screening of donors for infectious diseases and for other factors or behaviours that could increase the risk of an infectious disease being present,'' Saindon wrote. "The regulations further state that any imported semen must be accompanied by documentation showing that it is in compliance with the Canadian regulations.''

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

Palermo said that the decision has not had a big impact on their patients.

"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.''