Intracavernosal injection of PGE1 succeds in promoting a sustained penile erection in 70% of men.Porst reported a recovery of spontaneous erection after 3 months of PGE1 in 30% of men.Sahenz de Tejada hypotizes the recovery to be due to an improved NO production.Nitric Oxide is released by endothelium lining in response to various chemical (e.g. Achetilcoline) or physical (e.g. shear stress) stimuli.Penile erection is promoted by cAMP and cGMP pathways leading to phosphorilation of proteinkinase A and G respectively and relaxation of smooth muscle cells.Nitric oxide is involved in cGMP pathway, NO synthase strictly depends upon blood oxigen levels and according to literature PG E 1 intracavernosal injection may enhance penile oxigen pressure improving NO synthase activity and NO cavernosal levels.In the present study NO cavernosal levels were assessed before and after intracavernosal Pg E 1 injection in 30 men divided into three group according to penile color doppler flowmetry.The assessment employs nitrate redutase enzyme converting nitrates into nitrites and Griess reactive shifting into a red nitro compound read by spectrophotometer (wave-lenght 540 μ).