Transurethral resection of the prostate (TURP) is the only recognized treatment in patients with benign prostatic hyperplasia (BPH). Transurethral hyperthermia (TUHT) was used as an alternative treatment in patient who refused TURP. From 1987 to 1988, 21 BPH patients with moderate to severe symptoms and signs of prostatism were treated with TUHT in a phase I trial. Mean pre-treatment subjective and objective values were: total symptom score (TSS) 13.5, obstructive symptom score (OSS) 6.5, irritative symptom score (TSS) 7.0, peak flow rate (PFR) 11.6 cc/sec, post-voiding residual volume (PRV) 187 cc, and prostate volume (PV) 93 cc. TUHT was given for a total of 177 sessions (mean 8.4), each of 60 min duration at a steady state. Temperature was recorded continuously on the urethral surface, in all treatments. It ranged from Tmin 40.3 degrees C to Tmax = 49.2 degrees C and Tmean = 44.1 degrees C. The mean minimum temperature of > or = 42 degrees C was obtained in 98% of the TUHT sessions. Treatments were given on an outpatient basis without sedation or anaesthesia. Treatment tolerance was excellent with minor acute toxicity common (71% of patients), of no clinical importance and with no late complications. Of the 21 patients treated, 17 (81%) had an objective and 15 (71%) a subjective improvement recorded at 6 months post-treatment. This statistically highly significant improvement included: 61% decrease in TSS; 66% decrease in OSS; 55% decrease in ISS; 42% increase in PFR; 55% decrease in PRV; and 21% decrease in PV. Of the 17 patients with objective improvement, nine have maintained their response to TUHT for a minimum period of over six years, two relapsed at 11 and 40 months, respectively, and six patients died of cardiovascular causes maintaining their response to death. This study has demonstrated TUHT treatment efficacy with no major or clinically important toxicity in BPH patients. A relative weakness of this report is a lack of verification of objective study parameters in the patients at seven years post-treatment. Prospective randomized trials are needed to define the role of TUHT in the management of BPH patients.