This was designed to investigate possible potentiation of testosterone and dihydrotestosterone by estradiol and prolactin in augmenting weight and citric acid content of the rat lateral prostate. Using these parameters, the effect was assessed of estradiol and prolactin on 5.alpha.-reduction as it acts on the conversion of testosterone to dihydrotesterone. In the 1st part of the study, 87 castrate and 14 control rats were used to assess the effect of testosterone or dihydrotestosterone when supplemented with estradiol; in the 2nd part of the study, 121 castrate-hypophysectomized rats separated into 3 groups according to age and stage of maturation were used to assess the effect of prolactin in supplementing testosterone and dihydrotestosterone. Estradiol appears to have a greater effect on 5.alpha.-reduction than does prolactin; however, other pathways of androgen metabolism are altered by these agents. These alternate pathways are discussed.