The concentration of ofloxacin in prostatic tissue and serum was determined in order to evaluate the permeability of ofloxacin into prostatic tissue in patients with benign prostatic hypertrophy. Ofloxacin was administered orally at a dose of 200 mg several hours before subcapsular prostatectomy. The determination was performed in the surgically removed adenoma and in the serum taken one hour before and at the removal of the adenoma. The peak level in the prostatic tissue was 1.46 microgram/g at 4.5 hour after the administration. The ratio of prostatic tissue level to the serum level was 1.00. In conclusion, ofloxacin was thought to be very useful for the treatment of acute and chronic prostatitis.