A 37-year-old woman presented with a history of secondary amenorrhoea and hirsutism for 4 years. She had elevated serum levels of testosterone and dihydrotestosterone, and decreased serum levels of sex hormone binding globulin and oestradiol. Almost daily use of a testosterone-containing ointment in the vulvar region for 6 years was disclosed as the cause of the hyperandrogenism. Serum testosterone, testosterone excretion rate in urine and testosterone/epitestosterone ratio in urine were determined at fixed intervals 24 h before and 48 h after application of the testosterone-containing ointment. There was a rapid increase in serum testosterone, with a peak level after 4-6 h. The testosterone excretion rate and the testosterone/epitestosterone ratio in urine peaked after 2-4 h. After 48 h the serum testosterone level was still about twice the basal value. The testosterone/epitestosterone level was over the 'doping limit' of 6 for 28 h. We conclude that determination of the testosterone/epitestosterone ratio in urine would have disclosed exogenous testosterone administration in this patient. We recommend this test for patients in whom exogenous testosterone administration is suspected.