The endothelial nitric oxide synthase (eNOS) gene is responsible for constitutive nitric oxide synthesis and arterial vasodilatation. Recently two polymorphisms, the 27-bp repeat sequence in intron 4 and the Glu298Asp substitution in exon 7 of the eNOS gene have been reported to be related to coronary heart disease (CHD). We screened these polymorphisms of the eNOS gene in 308 unrelated nondiabetic subjects with CHD, in 251 unrelated patients with type 2 diabetes with CHD, and in 110 randomly selected healthy subjects without CHD. The 4a and Asp298 allele frequencies of the eNOS gene were 0.19 and 0.36 in nondiabetic patients with CHD, 0.21 and 0.27 in type 2 diabetic patients with CHD, and 0.16 and 0.31 in nondiabetic subjects without CHD (n.s. between the groups). The Asp298 allele in exon 7 of the eNOS gene was not associated with elevated blood pressure in any of the study groups. Among type 2 diabetic patients with CHD the 4a allele in intron 4 of the eNOS gene was associated with elevated levels of systolic (P=0.035) and mean arterial blood pressure (P=0.040). In nondiabetic subjects these associations were not statistically significant. When all study groups were pooled in statistical analysis the 4a allele of the eNOS gene was associated with elevated diastolic (P=0.032) and mean (P=0.030) arterial blood pressure even after adjustment for confounding factors. We conclude that the 4a allele of the eNOS gene is not associated with CHD or type 2 diabetes, but that it is related to elevated blood pressure levels particularly among type 2 diabetic patients with CHD.