Functional ovarian hyperandrogenism (FOH) is characterized by an abnormal ovarian response to challenge with the GnRH analogs nafarelin and leuprolide acetate, similar to that observed in women with well defined polycystic ovary syndrome, regardless of whether elevated LH levels or polycystic ovaries are present. We studied an unselected group of 42 hyperandrogenic adolescents (age range, 14-22 yr; mean, 18.1 +/- 2.5 yr) 1) to determine FOH incidence through the assessment of ovarian-steroidogenic response to a single dose of leuprolide acetate, 2) to assess the clinical characteristics of patients according to their responses to GnRH analog stimulation, and 3) to evaluate adrenal steroidogenic function and its relation to ovarian hyperandrogenism in patients with either normal or abnormal responses to leuprolide acetate challenge. All patients underwent leuprolide acetate and ACTH testing, dexamethasone and ovarian suppression tests, and pelvic ultrasonography. Twenty-four (58%) patients had supranormal plasma 17-hydroxyprogesterone (17-OHP) responses to leuprolide acetate characteristic of FOH, and in 18, the 17-OHP response was similar to that of controls (n = 24; age, 17.1 +/- 2.3 yr). Seven patients (5 with FOH and 2 with normal responses to leuprolide acetate) had an abnormal response to ACTH, but only 1 had conclusive evidence of 21-hydroxylase deficiency. In 16 patients, the response to both stimulation tests was normal. Only 13 (54%) of the 24 FOH patients had polycystic ovaries on ultrasonography, and in 11 (46%), basal plasma LH levels were elevated. In FOH patients, reduction in testosterone and androstenedione plasma levels was significantly greater after ovarian suppression than after dexamethasone challenge (P < 0.0005 and P < 0.02, respectively). Peak plasma 17-OHP levels postleoprolide acetate simulation correlated with dexamethasone-suppressed plasma testosterone concentrations, dexamethasone-suppressed plasma androstenedione levels, and the free androgen index postdexamethasone treatment (r = 0.4, P = 0.01; r+ 0.4, P < 0.05; and r = 0.41, P = 0.007, respectively), Plasma sex hormone-binding globulin levels after dexamethasone administration correlated negatively with the baseline free androgen index (r = -.0.67; P < 0.0001). Considering our diagnostic criteria, 26 (62%) of our collective of 42 patients had abnormal responses to one or both stimulation tests, whereas 16 (37%) had normal response. FOH is the most common cause in (58%) of androgen excess in adolescence. Short term leuprolide acetate stimulation is a reliable tool fro identification of the ovary as the source of their hyperandrogenism.