American soldiers are taking an unusual precaution before heading to the Persian Gulf, fearing that powerful vaccines or exposure to biological weapons might affect their fertility.

They're freezing their sperm.

Sperm banks nationwide have reported an increase in the number of military clients as deployment orders rapidly increase.

"It doesn't protect their life. It doesn't protect them from illness. But at least ... a man can beget a legal heir," said Dr. Cappy Rothman, co-director of California Cryobank.

In January, 28 soldiers had their sperm frozen in liquid nitrogen at the company's three sperm banks in California and Massachusetts. That was a sharp increase from the firm's two military clients in 2001, and the 12 in 2002 that lab officials attributed to the deployment of troops to Afghanistan after Sept. 11.

Labs elsewhere in the country also reported increased business.

"It has really picked up in the last few weeks," said Brent Hazelrigg, program director for the Genetics and IVF Institute in Fairfax, Va. "We have men who are coming in and producing a specimen and then shipping out the next day."

The firm's three sperm banks in Texas, Virginia and Minnesota saw a total of 12 soldiers in January. In all of 2002, the labs had seven military clients.

Patrick Atwell, a 35-year-old mechanic from central California and a member of the Army National Guard, saved his sperm at the urging of his fiancee, a nurse.

"If I do come back, and I am sterile from what they exposed us to, it's really not a big thing now because we can have a baby," he said.

Atwell's fiancee, Angela Cruz, 36, said the move was about "having a reminder of him, having another person carry his name, his being."

"If something does happen to him, I will definitely be making a withdrawal from the bank," she said.

Many of the soldiers are turning to the labs after hearing horror stories about the tactics of Iraqi leader Saddam Hussein and reports of fertility problems from veterans of the Gulf War.

Military officials, however, said fears about vaccines are unfounded.

"We just don't have any medical indication that there is something to be concerned about," said Dr. Michael Kilpatrick, deputy director of the military's office of deployment health support.

Kilpatrick served as an adviser during the military's investigation of Gulf War illnesses.

A recent study by researchers at Duke University Medical Center found reduced sperm production in rats exposed to three chemicals used to protect Gulf War soldiers from insect-borne diseases and nerve-gas poisoning.

Military officials discounted the study, saying soldiers were not exposed to the three chemicals simultaneously or for an extended period of time. In addition, the study did not determine if the effects on the rats were temporary or long-term, Kilpatrick said.

Soldiers routinely receive shots for the flu, diphtheria, tetanus and typhoid fever before shipping out. Depending on where they are being deployed, the soldiers may also receive vaccinations against smallpox and anthrax.

Sperm banks are typically used by cancer patients and men about to undergo a vasectomy. The process involves obtaining sperm and freezing it in liquid nitrogen at about 320 degrees below zero.

The sperm can be stored indefinitely without any effect on its potency, experts said. First-time fees range up to $200, and the average annual storage cost is about $300.

"We kind of look at it as fertility insurance," Hazelrigg said. "They know it's there. They know it's safe. It provides them peace of mind."