Androgens are an essential prerequisite for the development of acne. The present study was undertaken to characterize the androgen status of women with late onset and persistent acne only and, using the dexamethasone (dex) suppression test, to identify the source(s) of the androgen excess. We measured serum levels of total testosterone (T), free testosterone (FT), androstenedione (A4A), dihydrotestosterone (DHT), dehydroepiandrosterone sulphate (DHEA-S) and sex hormone binding globulin (SHBG) in 34 healthy control subjects, in 34 women with mild acne and in 29 women with moderate or severe acne. Serum FT, DHT and DHEA-S levels in patients of both acne groups were significantly higher than those in the control subjects. The other hormone levels showed no significant differences between patients and control subjects, and there were no significant differences between the two acne groups in any of the androgen levels. In order to evaluate the ovarian and adrenal contributions to serum androgens in the acne patients, the serum levels of A4A, T, DHT and DHEA-S were measured prior to and following 2 weeks of dex therapy. Following the dex test, the DHT and T of adrenal origin were significantly higher in the acne patients than in the control subjects. These results suggest that, in acne patients, hyperandrogenaemia is likely to develop as a result of adrenal androgen excess. In addition, since abnormally high androgen levels are frequently seen in late onset and persistent acne, it seems that this condition is likely to be a sign of hyperandrogenism.