In the present study, the effects of maternal ethanol intake during pregnancy on microsomal cytochrome contents and on enzyme activities in the developing fetus were investigated. Ethanol intake to pregnant females did not affect the maternal body weight or number of fetuses, but tended to reduce the mean fetal body weight, especially the fetuses from a litter of mother who were treated with ethanol during day zero to 20 of gestation showed significant decreases in the body and liver weights. No significant changes were observed in the contents of cytochrome P-450 and b₅ and the activities of NADPH-cytochrome c reductase and heme oxygenase in the livers of fetuses whose mothers were exposed to ethanol during pregnancy when compared with that of untreated pregnant rats. However, NADH-cytochrome b₅ reductase activity in the fetal livers was found to significantly decrease by maternal ethanol intake during pregnancy.