This study was done to evaluate the effectiveness of transdermal nitroglycerin in the treatment of erectile dysfunction in males with spinal cord lesions as compared to the treatment with intracavernous injection of papaverine. The study design used was an open, randomized, cross over trial of intracavernous injection papaverine versus transdermal nitroglycerin. Twenty eight male patients with spinal cord lesions with erectile dysfunction were included in the study, and were subjected to intracavernous injection of papaverine and transdermal nitroglycerin with an interval of 2 weeks as the wash out period. Objectively, the times taken for the onset and the duration of erection were noted. The length of the penis and its circumference at its base were measured at intervals until the erection subsided. The volume of the penis at the onset and at the peak of erection was calculated. Twenty six patients (ie 93%) who received an injection of papaverine, and 17 (ie 61%) of the patients who received nitroglycerin showed a complete response. The difference was statistically significant (P = 0.004). Nine (32%) patients had complications with the injection of papaverine. The only complication noted with the application of a nitroglycerin patch was mild headache, experienced by six (21%) patients. It was concluded from the study that intracavernous injection of papaverine is more effective than transdermal nitroglycerin in the treatment of erectile dysfunction in patients with spinal cord lesions.