Detection of endothelial nitric oxide synthase gene expression in patients with organic erectile dysfunction. The study involved 24 male patients complaining of failed sexual intercourse for at least six month and were indicated for penile prothesis. Biopsy was obtained from cavernous tissue and was subjected to Reverse- Transcriptase, Polymerase Chain Reaction for detection of endothelial nitric oxide synthase gene expression. Twenty–four male patients were evaluated. There was no significant difference in endothelial nitric oxide synthase gene expression in those patients regarding various risk factors as diabetes mellitus, hypertension or severity of the erectile dysfunction. Also there was no significant correlation between endothelial nitric oxide gene expression with marriage duration, complaint duration or age of the wife. The results demonstrated that endothelial nitric oxide synthase gene expression has no clinical significance as to evaluate erectile dysfunction.