The genesis of benign prostate hyperplasia (BPH) depends on two factors: testicular androgen and the aging process. The most important androgen in the prostate is dihydrotestosterone (DHT). In the aging male the level of DHT in the prostate remains largely constant although the plasma level of testosterone decreases. DHT is formed by the reduction of testosterone by the enzyme 5-alpha-reductase, which has two isoenzymes. The 5-alpha-reductase type 2 is the predominant isoenzyme in genital tissue and thus also in the prostate. Finasteride is a 5-alpha-reductase inhibitor, which is applied in the treatment of BHP and male baldness. In the doses used finasteride acts mainly by inhibiting the 5-alpha-reductase type 2, thereby reducing the serum level of DHT by approximately 70% and by about 85-90% in the prostate. Indeed the effect of finasteride in BPH was proven in clinical studies. However, the circulating and intraprostatic DHT could be further reduced by a more effective dual 5-alpha-reductase inhibitor, which would be efficacious in the treatment of benign prostate hyperplasia and other DHT-related disorders.