First, it was tight pants. Then, it was saunas. Now, when it comes to fertility, men have something else to worry about: laptop computers.

Scientists at Stony Brook University Hospital on Long Island have discovered that the male testes heat up after only an hour of laptop use, and the 4.9-degree Fahrenheit increase may be enough to impair fertility.

Further tests are necessary to determine just how much heat would be detrimental to sperm, he said, and the next step is to measure sperm count before and after laptop use. Nevertheless, he said, he will add a new question to his medical evaluation when he sees patients dealing with infertility.

It's been long known that heat can damage sperm concentration and morphology, or shape. When couples arrive at a doctor's office with infertility problems, they fill out forms including such questions as whether the man takes hot baths or uses a sauna or has suffered a recent high fever. Occupational exposure to heat is also a concern, and bakers, pizza makers and truck drivers who spend time in hot cabs seem to be at greater risk, Sheynkin said.

The Stony Brook scientists recruited 29 healthy men who then spent an hour using a laptop on two separate occasions. Readings from a thermal device attached to each man's scrotum rose by 5.7 degrees Fahrenheit on the right side and 4.9 degrees on the left.

Previous studies by other scientists have shown that a 2-degree Fahrenheit change can disrupt sperm production. Computers give off a lot of heat. Sheynkin said that the laptop computer went from 87.6 degrees Fahrenheit at the start of a session to 103.8 degrees an hour later.

Dr. Daniel Kenigsberg, an infertility expert and director of Long Island IVF in Port Jefferson, agreed that it is important to understand all factors that could contribute to infertility. He said about 15 percent of couples have problems conceiving, which is linked to sperm quality about half the time.