BACKGROUND:Endothelial nitric oxide synthase produces nitric oxide which is involved in many physiologic regulatory functions. Variable number of tandem repeats in intron 4 of endothelial nitric oxide synthase gene are reported to be associated with blood pressure regulation. Nitric oxide is involved in regulation of cardiomyocyte genes but it is not known If endothelial nitric oxide synthase 4 gene polymorphisms are related with left ventricular hypertrophy. We studied endothelial nitric oxide synthase 4a/b allele status in hypertensive and normotensive patients and echocardiographic parameters in a subgroup of hypertensive group. METHODS:We performed a case-control study involving 110 Turkish hypertensive patients and 87 controls. All subjects were genotyped for endothelial nitric oxide synthase 4a/b polymorphism. Echocardiographic measurements were obtained in 94 of the hypertensive patients. RESULTS:Endothelial nitric oxide synthase 4a/b genotype frequencies were 6.4%, 23.6%, 70% in hypertensives and 1.1%, 18.4%, 80.5% in controls for a/a, a/b, b/b, respectively. Left ventricular dimensions, mass and diastolic indices were not different across endothelial nitric oxide synthase 4 genotypes. Patients with 4a/a genotype had higher interventricular septal thickness than the other group; 14.83(1.6), 11.91(1.51), 12.21(1.56) for a/a, a/b, b/b, respectively and p = 0.0001. CONCLUSION:Endothelial nitric oxide synthase 4a/b gene polymorphism is not associated with hypertension in Turkish patients. 4a/a genotype was associated with higher interventricular septal thickness in hypertensive patients.