The effect of maternal exposure to cigarette smoke on the fetus was studied by analyses of sister chromatid exchange (SCE) and formation of micronuclei with fetal liver cells. Fetal tissues were obtained from pregnant ICR/Jcl mice at the 16th day of gestation. Mice were exposed to mainstream or sidestream cigarette smoke with or without passage through filter (gas phase smoke or whole smoke). Each stream of smoke was used for three exposure schedules, i.e., short-term (two exposures at 15th and 16th day of gestation), long-term (exposure started at 4 wk before mating and stopped at 16th day of gestation), and prepregnant term (exposed for 4 wk before mating). The number of SCEs of fetal liver cells was significantly increased in all exposed groups. In the mainstream experiments, the long-term group showed a significant increase in the number of SCEs in comparison with that in the short-term group. Exposure to sidestream smoke increased the number of SCEs more than in groups exposed to mainstream smoke. This tendency was also recognized in the experiments with filtered smoke. On the contrary, no significant changes were observed by the micronucleus test. The transplacental genotoxic effect of maternally inhaled cigarette smoke was accurately detected by analysis of SCEs with fetal liver cells.