Nitric oxide is synthesized from L-arginine by endothelial nitric oxide synthase encoded by eNOS gene. This study was performed to investigate the relationship between the serum nitric oxide level and eNOS gene polymorphism in the Turkish population with angiographically diagnosed coronary artery disease (63.47 +/- 9.10 years old, n=250) and control subjects without any history and/or risk factors of coronary artery disease (60.71 +/- 9.14 years old, n=150). Griess assay and PCR-RFLP analysis were used to measure the serum nitric oxide metabolites and genotypes, respectively. It was found that Glu/Glu, Glu/Asp and Asp/Asp genotype frequencies of the eNOS were 49.3%, 41.3% and 9.3% respectively in the control group, and 45.6%, 41.2% and 13.2% in the patient group. Serum nitric oxide levels were (32.56 +/- 17.26) muM in controls and (29.84 +/- 11.88) muM in patients. Neither the frequencies of the Glu298Asp genotypes nor the serum nitric oxide levels showed a significant difference between the groups. There was also no correlation between serum nitric oxide levels and the frequencies of the eNOS genotypes. Result showed that the coronary artery disease of the Turkish population seemed to develop without any alterations in eNOS Glu298Asp genotype frequency and the serum nitric oxide level.