Results: There was no statistically significant difference between the three groups regarding age, sex, hypertension, hypercholesterolemia, presence of diabetes mellitus smoking and family history of CAD (p>0.05). In comparing group A with group B, there was no statistically significant difference between the two groups regarding flow mediated dilatation (FMD)%, NTG mediated dilatation % and ratio of FMD to NTG mediated dilatation (p>0.05), but there was a highly statistically significant difference between group A and group C regarding FMD% and FMD: NTG ratio (p<0.01) and statistically significant difference between the two-groups regarding NTG% (p<0.05). In comparing group Band C, there was statistically significant difference between the two groups regarding FMD%, NTG% and FMD to NTG% ratio (p<0.05). The sensitivity, specificity and positive predictive value of FMD% :5 4.5% in relation to coronary angiogram for detection of CAD was (75%, 80% and 88%) respectively. Regarding the effect of risk factors on FMD %, FMD % was significantly decreased in smokers, diabetic and hypertensive (p<0.05). Also it was decreased in hypercholesterolemic (p<0.01). However it was decreased in obese and those with positive family history but the difference was not statistically significant (p>0.05). Conclusion: The determination of endothelial dysfunction expressed by FMD % was found to be a sensitive and specific screening test to predict the presence of CAD. Because this is non invasive, non-radioactive and cost-effective approach, it warrant further evaluation to determine it is value in daily clinical practice as an additional screening test in diagnosis of CAD. Key Words: Coronary artery disease - Endothelial dysfunction