In order to investigate the effect of Danazol (D) on serum prolactin (PRL) and cortisol levels, D was given orally in a daily dose of 400 mg for 2 weeks to 4 women (400 mg group) and 600 mg to 5 women (600 mg group) at one month and more after menopause and oophorectomy. The blood samples were taken through an indwelling catheter into the cubital vein every 20 minutes for 2 hours before and after the administration of D. Serum hormone levels were determined by each specific RIA. In a comparison in each individual of mean hormone levels of 7 serum samples before and after D, (1) serum PRL levels were significantly lowered in 2 women after D of 400 mg (p less than 0.001) and in one woman after D of 600 mg (p less than 0.001), but increased in one woman after D of 600 mg (p less than 0.001), (2) serum cortisol levels were significantly lowered in one woman after D of 400 mg (p less than 0.01) and in 4 women after D of 600 mg (p less than 0.001). When the mean hormone levels in the 400 and 600 mg group (an average of the mean hormone levels of 7 samples in each group) were compared before and after D, (1) the mean serum PRL levels were not significantly affected by D in either group, (2) the mean serum cortisol levels were significantly lowered by D in the 600 mg group, but not in the 400 mg group. The present study demonstrated that serum PRL levels were not consistently affected by D in the condition without ovarian hormones, and serum cortisol levels were lowered after a relatively larger dose of D.