Abstract. Hyperprolactinaemic patients occasionally demonstrate hirsutism and elevated levels of DHA-S, a weak androgen of adrenal origin. Abnormal adrenal function is frequently observed in hirsute patients. These observations prompted speculation that prolactin may modulate normal adrenal secretion and that derangements of adrenal androgen secretion may be due to abnormalities in prolactin. In this study we examined the possibility that elevated prolactin levels may be involved in the pathogenesis of hyperandrogenaemia in hirsute patients. However, basal prolactin levels in hirsute women, with or without menstrual disturbances, 201 ± 24.3 mU/l (mean ± se) and 192 ± 24.3 mU/l respectively, were significantly suppressed below levels in normal women, 289 ± 12.2 mU/l. The prolactin responses to stimulation with TRH and to suppression with l-dopa were also studied in hirsute patients. The prolactin response to TRH (maximum increment or integrated response) was exaggerated significantly in hirsute women with menstrual disturbances when compared to normal women, to hirsute women with normal menses or to normal men. This abnormal response may have been due to elevated oestrone levels present in patients with oligomenorrhoea (318 ± 49.5 pmol/l compared to 191 ± 12.1 pmol/l in normal women and 161 ± 15.5 pmol/l in hirsute women with normal menses, P < 0.05). There were no abnormalities detected in the suppression of prolactin in response to l-dopa in any of these groups. These findings do not support a role for prolactin in the pathogenesis of hyperandrogenaemia in hirsute patients. However, elevated androgen levels in women may bring about suppression of basal prolactin levels to values seen in normal men. In addition elevated oestrone levels may exaggerate the stimulatory effect of TRH on prolactin secretion. as was seen in oligomenorrhoeic hirsute women.