Ketoconazole, an imidazole derivative, is a large spectrum antifungal agent. The drug is known to cause a decrease in plasma androgens and adrenal steroids in normal men; it is also an active drug in the treatment of malignant tumors of the prostate. To examine the anti-androgenic action of this drug in women, we measured several gonadal and adrenal steroids in 21 normally menstruating women before and after receiving oral ketoconazole (200 mg twice daily) for 5 days. Plasma testosterone (T) decreased from a basal level of 0.35 to 0.25 ng/mL（± SEM) (P < 0.001); dihydrotestosterone (DHT) from a basal level of 190.62 ± 23.2 to 159.75 ± 19.43 pg/ mL (P < 0.02); dehydroepiandrosterone sulphate (DHEA-S) from 1.42 ± 0.44 to 1.15 ± 0.19 μm/mL (P < 0.02). Plasma 17β-estradiol (E₂) decreased from a basal level of 97.42 ± 29.37 to 54.32 ± 9.9 pg/mL (P < 0.05). In contrast, plasma 17-0H-progesterone (17-0HP) levels increased from a basal level of 44.81 ± 8.21 to 71.81 ± 15.81 ng/100 mlL (P < 0.05). These results confirm that the ketoconazole blocks the conversion of progestins into androgens. The decrease in the plasma concentration of E₂ suggest a direct effect of the ketoconazole on the ovary. It is likely that the effect of the drug, both at the level of the ovaries and of the adrenal gland, is dose-dependent. the new therapeutic approach to hormone-dependent tumors in men using ketoconazole opens intersting therapeutic possibilities in women, such as a nonhormonal antiandrogen m certain dysfunctional pathological conditions and in the treatment of hormone-dependent tumors and hormone-secreting tumors women.