Chronic prostatitis is possibly the most common infectious disease in middle-aged men. Clinical investigation was made on 24 outpatients with chronic prostatitis at our department, during the period of October, 1983 to August, 1984. The diagnostic criterion of the prostatitis was detection of more than ten leukocytes per high power field on microscopic examination of the expressed prostatic secretion and urine after prostatic massage. Twenty-four patients with chronic prostatitis were treated with 2 tablets of Dolcol (Pipemidic acid, PPA) three times daily for 7-30 days. The effectiveness was evaluated by improvement of subjective symptoms and objective findings. The results of the therapy with PPA on chronic prostatitis were excellent in 8 patients (33.3%), good in 10 (41.7%), fair in 2 (8.3%), and poor in 4 (16.7%). The effective rate was 83.3%, while no side effects were noted. Therefore, PPA was suggested to be effective against chronic prostatitis.