The safety and efficacy of transurethral microwave thermo-therapy (TUMT) for the treatment of symptomatic benign prostatic hyperplasia (BPH) have been demonstrated in the urological literature. Since a radiofrequency electromagnetic wave has deeper and more even transmission of heat to tissues than a microwave, we have developed a new prototype device for transurethral thermotherapy using a radiofrequency electromagnetic wave. The device consists of a microcomputer-controlled heat generator operating at 8 Mhz, a temperature monitoring system, a urethral cooling system and a urethral applicator and a rectal thermosensor probe. A balloon electrode encased in a specialized Foley catheter is connected parallel to twin plate electrodes on both sides of the pelvic region. An 8-MHz electromagnetic wave is directed to the prostate by means of capacitive coupling. The water coolant continuously perfused through the catheter allows high temperatures within the prostate while preserving the urethral mucosa. Heating experiment using agar phantom showed the hot spots to be distributed at 0.5-3 cm from the catheter surface. Heating experiment using canine prostates demonstrated that an intraprostatic temperature of > 48 degrees C could be achieved while the urethral and rectal temperatures had not exceeded 36 and 40 degrees C respectively. Histological examination immediately after the experiment showed the urethral mucosa to be preserved while coagulation necrosis of the periurethral prostate accompanied with congestion and hemorrhage of small blood vessels were observed at 5-8 mm from the urethra. The bladder and the rectum showed no gross alterations. Histopathological examination 10 days after the experiment revealed the intact urethral mucosa and mild mononuclear infiltration around the destroyed periurethral glands.(ABSTRACT TRUNCATED AT 250 WORDS)