In our study, one hundred patients complaining of erectile dysfunction recruited from andrology clinic, Cairo University. Another group of one hundred healthy individuals was taken as a control. The following was done to every patient: History taking, Clinical examination, Fasting, 2 hours postprandial blood sugar, and glucosulated haemoglobin, Duplex scanning of cavernosal arteries, Regisican monitoring for 3 days. Then blood collection with intravenous cannula was inserted into cubital vein.Then after a period of self-stimulation, a butterfly needle was inserted percutaneously into corpus cavernosum. Then determination of plasma level of NO2-/NO3- levels by Griess reaction according to Guevara et al,1998 protocol. Patients were divided into psychogenic group: 22 cases andorganic group 78 cases, which were further, classified into two sub groups into: diabetic cases: 37 cases and non-diabetic: 41 cases. the results were as follows: There was a significant decrease of both systemic and cavernous total NO2-/NO3- levels with increase of age in both patient and control groups (P value<0.001). There was a significant increase in systemic total NO2-/NO3- levels in controls compared to patients (P value<0.001). There was a significant increase in both systemic and cavernous total NO2-/NO3- levels in psychogenic group compared to organic group and non-diabetic group compared to diabetic group (P value<0.001) with a significant correlation between both systemic and cavernous total NO2-/NO3- levels and PSV, glucosulated haemoglobin ,response to ICI and percentage of cavernous artery increase in diameter after ICI as measured by penile duplex (P value<0.001). We recommend measuring total NO2-/NO3- levels is helpful in workup of erectile dysfunction to differentiate psychogenic from organic cases, assessment severity of affection of arterial hemodynamics and to asses some risk factors of erectile dysfunction as diabetes mellitus and aging. Measurement of systemic levels can give comparable to cavernous levels studying erectile dysfunction study but less invasive so can surpass its use.