Prostalase¿ has a probe that emits a laser beam at 360 degrees . Targeted obstructive prostatic adenoma tissue was heated to above the cytotoxic threshold temperature of 45 degrees C. After successful canine prostate study, from September 1992 to April 1993, 45 patients were treated. This paper reports the 9 months results of this initial cohort of patients. Prostatic and periprostatic temperature mapping showed the mean temperature within the adenoma zone was 49 degrees C, while the periprostatic tissue remained within the safety level of less than 42.5 degrees C. The mean prostate volume reductions at 3, 6, and 9 months were 36, 33, and 38%, respectively. Those patients whose surgery was unsuccessful had prostatic tissue removed by TURP at 2 to 3 months. This tissue revealed a definite zone of coagulative necrosis. For the clinical assessment, patients were divided into urine retention (UR) and nonretention (NR) subgroups. At 9 months, 20 of the 32 UR subgroup and 10 of the 13 NR subgroup patients were available for assessment. Due to poor response or complications, 6 of the 26 UR patients (23%) required ancillary treatment. Hence, 20 of the 26 cases (77%) remained catheter free and their mean maximum uroflow +/- SE was 9.6 +/- 0.7 ml/sec. Based on a Siroky normogram only 7 of these 26 patients (27%) became unobstructed. Two of the 12 NR subgroup patients (17%) required ancillary treatment. The mean maximum uroflow +/- SE was 10.7 +/- 1.2 ml/sec.(ABSTRACT TRUNCATED AT 250 WORDS)