Amniotic fluid androgen and estrogen levels associated with 48 male and 72 female fetuses between 14 and 20 weeks of gestation were measured. Amniotic fluid testosterone levels were significantly higher (P less than 0.001) in the male (224 +/- 11 pg/ml) than the female fetuses (39 +/- 2 pg/ml) with no overlap of values. Amniotic fluid androstenedione concentrations were also significantly higher (P less than 0.001) with male (1024 +/- 53 pg/ml) than female fetuses (668 +/- 39 pg/ml), but there was overlap. There was no difference between anmiotic fluid dehydroepiandrosterone levels for the two sexes. Estrone concentrations were slightly but not significantly higher with the male (353 +/- 33 pg/ml) than with female fetuses (331 +/- 28 pg/ml), while estradiol concentrations were significantly higher (P =0.002) with the female (96 +/- 8 pg/ml) than male (64 +/- 4 pg/ml) fetuses. It is interpreted that the higher amniotic fluid testosterone and androstenedione levels for the male fetuses reflect fetal testicular secretion. The significantly higher estradiol concentrations for the female fetuses may reflect early ovarian secretion.