Medroxyprogesterone acetate (MPA), 5 micrograms/g body wt, was given to lactating female rats 1 day after parturition. Group 1 females suckled 10-12 young, with equal numbers of males and females, while Group 2 females each suckled 10 female young. The young were weaned at 21 days of age. Exposure to MPA advanced the day of vaginal opening by 1 day, and increased anogenital distance in Group 2 young. At autopsy between 80 and 100 days of age, the clitoris of Group 2 females was significantly greater than in controls, and ovarian and adrenal weights were reduced.