Environmental tobacco smoke (ETS) contains relatively high concentrations of polycyclic aromatic hydrocarbons (PAHs). Urinary 1-hydroxypyrene (1-OHP), a metabolite of pyrene, is a good indicator of PAH exposure in occupational studies. In this study, we investigated the relationship between urinary 1-OHP concentration and ETS exposure in preschool children. Forty preschool children, aged 24-76 months, were studied during November and December, 1999. Two spot-urine specimens (one in the morning immediately after the subject woke up and the other at night before the subject went to bed) were collected 1 day after completion of a questionnaire, in order to determine 1-OHP concentrations by fluorescent spectrophotometry. Overall, urinary 1-OHP concentrations were relatively low but detectable (morning: median, 0.021 microg/g creatinine; range, 0.002-1.019 microg/g creatinine; night: median, 0.015 microg/g creatinine; range, 0.002-1.328 microg/g creatinine). Multiple linear regression analyses revealed that the total number of cigarettes smoked by the children's fathers during the 3 days prior to collection of the urine specimens was significantly associated with their urinary 1-OHP concentrations, after adjusting for other confounders. Each cigarette smoked by a child's father resulted in an average 9.6% increase in 1-OHP concentration in the morning urine specimen (95% confidence interval = 1.8-18.1%; p = 0.02). We did not find a significant increase in the 1-OHP concentration in night urine specimens (p = 0.19). Although the sample size was small, these findings indicate that urinary 1-OHP may be a suitable biomarker of ETS carcinogen exposure in children.