We investigated whether plasma androstanediol glucuronide (ADG) levels reflect the increased androgenicity in women with idiopathic hirsutism (n = 24) or hirsutism associated with polycystic ovary syndrome (n = 10). We also evaluated whether ADG levels parallel the clinical evolution of the hirsutism during a combined treatment, with cyproteroneacetate (2 mg) and ethinylestradiol (35 micrograms), of women with moderate idiopathic hirsutism. Finally, we investigated if there is evidence for increased conversion of precursors to ADG in hirsutism, by comparing the ADG levels, measured by RIA, to ADG levels obtained by applying the conversion rates of precursors obtained in non-hirsute women. ADG levels were increased in less than half of the patients with mild hirsutism. The clinical cure of hirsutism, which was obtained by the treatment in majority of patients, was accompanied by a significant decrease of plasma ADG levels, but a similar decrease was also observed in the 5 patients who did not respond to treatment. The data show that, although there is evidence for increased conversion of precursors to plasma ADG in mildly hirsute women, the latter is not a reliable parameter of androgenicity. Our data suggest, moreover, that treatment with cyproterone acetate and ethinylestradiol decreases 5 alpha-reductase activity, as indicated by the more important decrease in ADG levels than in the precursors.