Using chlormadinone acetate (CMA) as the control drug, a double-blind study was carried out to examine not only the effects of 17 alpha-acetoxy-6-chloro-2-oxa-4,6-pregnadiene-3,20-dione (TZP-4238;) on subjective urinary symptoms but also, especially, that on the sexual function in patients with benign prostatic hypertrophy (BPH). The clinical efficacy rate in relation to the subjective urinary symptoms was about the same in the two treatment groups; 45.9% in the TZP-4238 group and 50.0% in the CMA group. However, the incidence of adverse effects on the sexual function showed a marked difference between the two groups. The TZP-4238 group revealed a lower suppressive effect on the function than the CMA group (45.1% vs. 71.4%). In relation to their causation of other adverse effects, there were no differences between the two drugs. Accordingly, in consideration of the facts that TZP-4238 with less influence on the sexual function affords a superior quality of life to elderly patients, while achieving effective treatment by means of a convenient single daily administration, TZP-4238 was surmised to be a more useful drug than CMA as an antiandrogen for the treatment of BPH.