Motility and selective migration of X- and Y-bearing human spermatozoa were studied in the presence of physiologic levels of sex steroid hormones (17beta-estradiol; estriol, 0.5 ng/ml; testosterone; progesterone; lynestrenol; and norgestrel, 5 ng/ml) and 200-fold higher concentrations. Estrogens and, to a smaller extent, testosterone accelerated spermatozoal migration, while gestagens had an inhibitory effect. 17beta-Estradiol was most effective in stimulating the motility of human spermatozoa, while norgestrel caused the strongest inhibition of forward movement. Migration of X- and Y-bearing spermatozoa was most significantly altered after longer distances of migration, shown by an increase in the percentage of Y-bearing spermatozoa from 43.7% to 63.3% at a distance of 90 mm. However, prolongation of migration time to 36 hours caused a reduction in the percentage of Y-bearing spermatozoa at the 90-mm distance, from 63.3% to 46%. Specific differential effects of sex steroid hormones on the pattern of selective migration and the distribution of X- and Y-bearing spermatozoa were not observed.