A 56-year-old woman presented with marked hirsutism and virilization of gradual onset. Menstruation had ceased at 43 years. The serum testosterone was grossly elevated (49 nmol/l) with levels of estradiol well above the postmenopausal range (200 pmol/l). Both serum testosterone and estradiol levels showed a marked but transient increase during the administration of the GnRH analog, buserelin. This indicated that the release of these steroids was under gonadotropin control. Bilateral oophorectomy revealed a greatly enlarged left ovary, and histology demonstrated a leiomyoma of the ovary with marked thecal reaction, which was probably responsible for the elevated serum testosterone and virilization. Testosterone levels returned to normal after bilateral oophorectomy. Excessive thecal androgen production associated with non-epithelial ovarian tumors is extremely uncommon and the response to buserelin has not previously been reported.