Antiandrogen therapy for benign prostatic hyperplasia (BPH) and prostatic carcinoma has been introduced in clinical practice. Steroidal antiandrogens such as progestational agents suppress prostatic growth through pituitary gonadotropin suppression as well as by blocking intraprostatic androgen action. Although clinical efficacy of the therapy appears to be promising in some clinical trials, the side effect of sexual function disturbances remains to be solved especially in BPH patients. The new treatment modality for advanced prostatic carcinoma has been introduced; the total androgen blockade therapy, utilizing a pure antiandrogen (Flutamide) in combination with an LH-RH agonist, has been proposed by some authors, but the overall efficacy has not been established yet. Clinical trials for two pure antiandrogens (Flutamide and Casodex) are currently in progress in Japan.