Use of the antiandrogen cyproterone acetate in the treatment of hirsutism.--25 women with hirsutism or hypertrichosis faciei were subject to a "reverse sequential therapy" with cyproterone acetate (Hammerstein's regimen) for 1 to 3 years. In 8 patients, a limited, in 14 patients a satisfactory and in one woman a good result could be recorded. Cycle irregularities and subjective side effects were within a tolerable range. Studies of the hair pattern in 15 patients revealed a higher telogen rate as well as increased diameters of the hair stalks, compared with controls, in the temporal region of the head. These alterations disappeared in the course of the treatment. In the parietal region of the head no significant differences of the hair pattern were found in comparison with the controls and during application of the steroids.