['Maternal environmental tobacco smoke (ETS) has been identified as a key risk factor for problem behavior in children, but the role of genetic susceptibility is not clear. The purpose of this study was to examine the metabolic genetic modification effect of exposure to ETS in nonsmoking mothers on child behavior at 2 years of age.', "A prospective cohort study was conducted among 191 mothers who gave births between 2004 and 2005 and their infants in Taiwan. The mothers completed a questionnaire before delivery in which they provided information on exposure to ETS during pregnancy. Four metabolic genes, CYP1A1 MspI, CYP1A1 Ile462Val, GSTT1, and GSTM1 were isolated from both maternal and infant DNA samples. Children's behavior problems at 2 years of age were reported by their mothers using the Child Behavior Checklist/1.5-5. Multiple linear models were used to estimate the effects of ETS and genotype on child behavior.", 'Maternal ETS exposure was associated with the anxious score. The ETS-exposed group with both the CYP1A1 MspI and the CYP1A1 Ile462Val variants had higher scores, as reflected in total CBCL score as well as scores on the internalizing scale and its emotional subdomain, the anxious scale, and the externalizing scale and its aggressive subdomain.'] Does cYP1A1 modify the effect of maternal exposure to environmental tobacco smoke on child behavior?