Systemic lupus erythematosus and rheumatoid arthritis are chronic,multifactorial autoimmune disorders where many genes have been tested forcarrying the risk of development or the progression of these diseases.The aim of the present study was to detect the prevalence of endothelialnitric oxide synthase (eNOS) genetic polymorphisms [ the 27-bp repeat inintron 4 and the SNP T-786C polymorphism in the promoter region] amongEgyptian SLE and RA patients and to study the influence of these geneticpolymorphisms on the clinical and laboratory features of these patients.In this study no statistically significant association could be foundbetween these genetic polymorphisms as risk factors of these two diseases orthe clinical features of the patients specially lupus nephritis. But we couldfind an association between the T-786C genetic polymorphism and theextra-articular manifestations of RA.