octors hoping to reduce the exposure of smokers' children to secondhand smoke have found that putting nicotine monitors in the home seems to help persuade parents to smoke less around their children.

Decreasing the levels of smoke is important because young children who live with a smoker have been found to be more susceptible to ear infections, asthma, bronchitis and pneumonia than those who do not.

In a study in the current issue of the journal Pediatrics, researchers from the Dana-Farber Cancer Institute, a Harvard affiliate, tried to change the habits of 291 low-income parents or caregivers in Boston and Providence over three years. The team installed nicotine monitors in the homes of the study's subjects as a way to measure the level of smoke in the air.

Next, the researchers used a technique known as motivational interviewing, in which the goal was to avoid overt persuasion but instead provide information that might make people change their behavior.

In this case, parents were informed that the monitors in their homes showed nicotine levels comparable to those of "the bar down the street."

"What do you think you might do?" the subjects were then asked.

Many of the people shifted their smoking to outside the home, or at least away from the rooms where their children spent a lot of time, the study reported. The researchers found that monitors recorded a decrease in nicotine of almost one-third.

The lead author, Dr. Karen M. Emmons, said the monitors proved that children's exposure to secondhand smoke could be reduced. Still, the researchers noted that even the lower levels of smoke posed risks.