PURPOSE: Lower urinary tract symptoms and erectile dysfunction (ED) are common disorders in men and increase with age. Recently, there has been evidence to suggest that patients with high benign prostatic hyperplasia symptom scores have an increased frequency of ED. This study was performed to evaluate the change of the expression of endothelin-1 (ET-1) in the corpus cavernosum by inducing partial bladder outlet obstruction (PBOO) in a rat model. MATERIALS AND METHODS: Eight Sprague-Dawley male rats were used for induction of PBOO by placing a 25 gauge angioneedle sheath around the urethra, then ligating the bladder neck with 3-0 vicryl suture and six sham-operated rats were ligated very loosely without causing obstruction. At three and five weeks after PBOO, the distal portion of the ligated penile tissues was dissected for immunohistochemical staining of ET-1 in the vascular endothelial cell. RESULTS: ET-1 was weakly expressed (+) in the smooth muscle layers of the control group and a very strong expressed (++++) in the experimental group on 3 weeks after PBOO. However, there was no expression in the experimental group on 5 weeks after PBOO. There was no expression (-) in the vascular endothelial cells of the control group and very strong expression (++++) in the experimental group on 3 weeks after PBOO. Howerver, there was no expression in the experimental group on 5 weeks after PBOO. CONCLUSIONS: The changes of penis by inducing partial bladder outlet obstruction in the rats were associated with increased ET-1 in the vascular and peri-vascular smooth muscle cells of the corpus cavernosum.