Children with asthma who are exposed to environmental tobacco smoke are at increased risk for adverse health consequences. An experimental design was used to evaluate a minimal-contact intervention aimed at modifying parents' smoking behavior in their homes. All subjects received counseling on the health effects of passive smoking and advice to quit smoking inside the home. Treatment subjects were also mailed the results of a urine cotinine test on their child and a self-help manual. More treatment (35%) than control (17%) subjects reported smoking outside their homes at posttest (and their children's cotinine levels were lower), but this difference was not statistically significant.