To study the effects of prolactin (PRL) on adrenocortical function in humans, dehydroepiandrosterone (DHA), dehydroepiandrosterone sulfate (DHAS), androstenedione (delta) and testosterone (T) were measured in serum obtained from 35 hyperprolactinemic women with galactorrhea and amenorrhea before and after treatment with bromocriptine-induced fall in mean PRL levels from 82 +/- 8 (SE) to 14 +/- 2 ng/ml (n = 39, P less than 0.0005), DHAS fell from 322 +/- 21 to 237 +/- 21 microgram/dl (n = 39); P less than 0.0005), DHA fell from 492 +/- 47 to 378 +/- 30 ng/dl (n = 39; P less than 0.01) while T (n = 16) and delta (n = 13) levels were unchanges (44 +/- 4 vs. 49 +/- 4 ng/dl and 280 +/- 55 vs. 236 +/- 40 ng/dl, respectively). In addition, 4 women were infused iv with 25 microgram synthetic ACTH over 4 h and serial blood samples drawn while hyperprolactinemic, and again 2-4 months later following normalization of PRL levels by bromocriptine. Although pre-infusion levels of DHAS were lower when PRL levels were normalized, no significant differences in responses of circulating DHAS, DHA, T, cortisol and 17-hydroxyprogesterone concentrations were detected between the two infusions. Since DHAS is virtually an exclusive product of the adrenal cortex, and since high PRL levels appear to inhibit ovarian steroid production, the findings suggest that hyperprolactinemia selectively stimulates adrenocortical androgen production.