Narrator: This is Science Today. Kent Pinkerton, a researcher at the University of California, Davis, is interested in the effect of second-hand smoke on unborn children. Since he can't blow smoke at humans, he uses pregnant rats.

Pinkerton: These mothers are exposed for six hours a day, five days a week.

Narrator: Pinkerton found that after they were born, the young of the mothers who'd been exposed to second-hand smoke had lungs that were unusually sensitive to second-hand smoke.

Pinkerton: They actually have hyper-reactive airways that is very similar to what we would see in an asthmatic condition. And that was a very striking finding because we never saw that type of response in any of the animals that had been exposed to cigarette smoke beginning from birth.

Narrator: Pinkerton's research is intriguing, because there's some evidence that human children born in smokers' households have an increased likelihood of developing severe asthma. He says that what's true for rats may be true for humans. For Science Today, I'm Steve Tokar.