In order to study the endocrine side-effects of danazol, 15 patients with severe, benign menorrhagias, were individually treated with this drug to stop bleeding. LH, FSH, testosterone, free testosterone, DES-S, androstenedione, prolactin, estradiol and cortisol serum concentrations were measured before and after the 3 month treatment period. Danazol was found to be effective in reducing the amount of bleeding in patients with benign, severe menorrhagias; however, the weight gain of patients was significant during the 3 month period. LH and estradiol concentrations decreased; testosterone, free testosterone and dehydroepiandrosterone sulfate increased; prolactin, FSH, androstenedione and cortisol serum concentrations did not change, and SHBG disappeared from the serum, during the treatment period. We are of the opinion that danazol is an effective drug in menorrhagias with side-effects. In our view the hyperandrogenicity is the most important side-effect of this substance, which might be the result of some metabolites, but which might be the effect of a peripheral action of the drug as well.