The possibility that hirsutism is an evolving syndrome rather than a static condition involving only one gland has been considered. To assess this proposal 60 untreated hirsute patients aged 12-32 years were divided into five groups according to the duration of the hirsutism (less than 1, 1-2, 2-3, 3-5 and greater than 5 years). Peripheral plasma concentrations of LH and FSH, androstenedione, dehydroepiandrosterone sulphate, testosterone, 5 alpha-dihydrotestosterone, 5 alpha-androstane-3 alpha, 17 beta-diol, 5 alpha-androstane-3 beta, 17 beta-diol, cortisol, oestradiol-17 beta and oestrone were determined by radioimmunoassay. When the values obtained were compared with those from normal menstruating women, the results showed that in group I there was a significant increase only in the mean plasma 5 alpha-androstane-3 alpha, 17 beta-diol concentration. The mean concentration of this steroid was also raised in all other groups. In groups II and III mean basal levels of plasma dehydroepiandrosterone sulphate were also significantly increased and showed a marked increase after ACTH stimulation (1 mg tetracosactide acetate, i.m.) as did the concentrations of androstenedione and 17 alpha-hydroxyprogesterone. Finally, in groups IV and V, a significant increase in mean plasma concentrations of LH, androstenedione, oestrone and testosterone was found in the basal condition. The clinical picture also became gradually more severe from group I to group V. These data suggest that hirsutism could be an evolving syndrome progressively involving peripheral androgen metabolism, the adrenal gland and finally the ovary possibly through alterations of hypothalamic-pituitary function.