The possible effect of medical androgen deprivation in the treatment of benign prostatic hyperplasia has been studied in 12 patients. Six patients received the luteinizing hormone-releasing hormone agonist buserelin and 6 others received the antiandrogen cyproterone acetate. The treatment resulted in an average decrease in prostatic size of 29 per cent after 12 weeks as measured by ultrasonography. This decrease led to an increase in peak urinary flow rate, a reduction in residual urine volume and a decrease in daytime voiding frequency. However, it caused no decrease in urethral resistance but only an increase in the bladder contraction strength. After discontinuation of the treatment the prostates showed regrowth to the initial sizes within 6 to 36 weeks. The urodynamic changes were reversed as well. Although statistically significant, the urodynamic changes were minimal from a clinical viewpoint and did not lead to an unobstructed state after 12 weeks of treatment. For this reason the clinical indication for use of medical androgen deprivation in benign prostatic hyperplasia patients will remain limited for the time being.