A total of 36 cases with chronic non-bacterial and non-chlamydial prostatitis or prostatodynia underwent 5 weekly, 1-hour sessions of transrectal microwave hyperthermia (43 degrees C) to the prostate. All patients had a long history of the condition and failed to respond to a variety of conventional treatments. The efficacy of the treatment was evaluated by the effects on subjective symptoms and/or on white blood cells in expressed prostatic secretions. Concerning the overall clinical efficacy, excellent results were obtained in 11 (30.6%), good in 8 (22.2%), fair in 8 (22.2%) and poor in 9 (25.2%). Although minor complications were noted in 5 cases (anal pain; 2, hematospermia; 1, hematuria; 1), all cases received full sessions. These results indicated the usefulness of the hyperthermia for this benign condition, which has so far responded poorly to the conventional therapy.