In the light of the high incidence of cardiovascular side effects with oestrogen therapy in patients with prostatic cancer, other medications altering androgen metabolism are under investigation. The influence of the anti-prolactin bromocriptin (CB157) on plasma kinetics of testosterone and on endogenous hormones was studied and compared with the effect of ethinyl oestradiol in 25 patients with prostatic carcinoma. Bromocriptine significantly suppressed both prolactin and testosterone, inhibited the transfer of androgen from the inner pool into the deep compartment and favoured its degradation. Ethinyl oestradiol decreased testosterone, LH and FSH, and prolonged the biological half-life of testosterone. The effects of bromocriptine on androgen metabolism might be of therapeutic value in patients with prostatic carcinoma.