OBJECTIVE: To study the effect of various concentrations of tobacco smoke exposure in the environment on cerebral apoptosis gene expression in pup rats in utero and postnatally. METHODS: Pregnant SD rats were exposed to air or to different concentrations of smoke for 5 hours daily, 7 days a week from day 2 of pregnancy until delivery. Then their pups were exposed to the same environment of passive smoking till weaning. Rapid competitive reverse transcriptasePCR was used to analyze the relative expression of Bax mRNA and Bcl-2 mRNA semi quantitatively of the cerebral hemisphere in the pups. RESULTS: The relative expressions of Bax mRNA of the cerebral hemisphere was 0.31 in the control group, 0.47 in the low concentration group, 0.55 in the moderate concentration group, and 0.60 in the high concentration group. It was significantly higher in the moderate and high concentration groups than that in the control group (P<0.05). The relative expressions of Bcl-2 mRNA were of no significant difference among the passive smoking groups and the control group. CONCLUSIONS: The increase of the relative expression of BaxmRNA in the pups' brain shows that cell apoptosis may play a role in brain damage of rats with passive smoking from intrauterine life to weaning.