Female rats were given 16% ethanol solution as the sole liquid during the entire period of gestation. At birth the offspring was removed and reared by foster dams consuming normal drinking water. When tested for feminine sexual behavior in adulthood, the males showed marked signs of feminization as evidenced by an increased amount of lordosis responses. No changes were seen in the masculine sexual behavior. No deviations were seen in the female estrous cycles or in onset of vaginal estrus, whereas the onset of behavioral estrus was delayed. It is suggested that prenatal ethanol exposure may lower the fetal testosterone production and thereby interfere with the normal course of sexual differentiation in the male.