The potency of 98 men who underwent transurethral resection for benign prostatic enlargement was assessed before and after operation in a prospective study. Preoperatively, 38 could not maintain their erections long enough to achieve coitus. Three months after operation a decrease in erectile ability had been experienced by three of the remaining 60 patients, while two reported an improvement. At the six-month follow-up two of these patients stated that they had recovered their preoperative potency, while the third patient still experienced reduced erectile function. Examination showed normal penile blood pressure but testing with papaverine showed reduced tumescence.