We tested a health education intervention program to reduce passive smoking in infancy. The aim was to develop an instrument for study of tobacco smoke exposure and childhood respiratory illness. One hundred and eighty-four women who had smoked during pregnancy were allocated by month of delivery to an intervention group, to a minimal contact group, or to a follow-up only comparison group. Exposure to smoke was assessed 3 months later by questionnaire and by measurement of cotinine in samples of maternal and infant urine. There was a reduction in maternal smoking associated with contact with research staff, but this was not statistically significant. There were no differences between the groups in the exposure of infants to tobacco smoke. Reasons for this finding may include the timing of the intervention, the heterogeneity of the target group, and the manner in which information was presented on health risks caused by parental smoking.