Hair nicotine levels were studied among children, relative to their caregivers' reported exposure to environmental tobacco smoke. A total of 117 children, aged 3 months to 10 years, were recruited consecutively from hospital inpatients, and their respective parents or caregivers were interviewed. Degree of exposure to environmental tobacco smoke was assessed via questionnaire. Scalp hair samples were collected from children and were assayed for nicotine. Levels of nicotine in hair among children reportedly exposed to smokers were higher than levels among unexposed children (chi2 = 26.46, p < .0001). In addition, hair nicotine levels were higher among children with mothers who smoked, compared with those whose mothers did not smoke. Whether household members smoked outside or inside the house had no significant effect on hair nicotine levels of children. Hair nicotine levels differed between children who were reportedly unexposed to environmental tobacco smoke at home and those who were exposed. Smoking outside the home, as reported by parents, did not cause a reduction in nicotine levels in the hair of children.