Abnormal regulation of cytochrome P450c17 alpha causes the exaggerated secretion of ovarian androgens in polycystic ovary syndrome (PCOS). This enzyme is active in both the ovaries and adrenal glands. We examined whether there is an abnormal regulation of cytochrome P450c17 alpha in the adrenal gland by investigating the relationship of 17-hydroxyprogesterone (17-OH progesterone) hyperresponsiveness to the gonadotrophin releasing hormone (GnRH) agonist, buserelin, testing with 17-OH progesterone response to adrenocorticotrophic hormone (ACTH) in PCOS, In all, 68 women with PCOS and 24 normal women were included in the study, Ultrasound, clinical and hormonal parameters were used to define PCOS, 17-OH progesterone response to ACTH was measured in all the women. In 52 of the 68 women with PCOS, 17-OH progesterone response to buserelin was measured, The mean basal 17-OH progesterone concentrations were similar in both PCOS and control groups, PCOS n omen had significantly higher net increment in 17-OH progesterone after ACTH administration (P<0.02). No significant correlations were found between the peak 17-OH progesterone values, the net increments in 17-OH progesterone and the area under the 17-OH progesterone-response curves after ACTH stimulation and buserelin test, Although 17-OH progesterone response to ACTH was significantly higher in the patients with PCOS than in the control subjects, the lack of relationship between 17-OH progesterone response to GnRH agonist buserelin and 17-OH progesterone response to ACTH stimulation suggests that the dysregulation of the cytochrome P450c17 alpha enzyme may not play a role in adrenal androgen excess seen in PCOS.