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The endothelial nitric oxide synthase (eNOS) gene is known to influence the regulation of blood pressure (BP) levels. However, whether the eNOS gene locus influences arterial stiffness independently of BP is unknown. This study examines the independent effect of the eNOS gene polymorphism (G894T) on arterial stiffness in 118 African American and 285 white young adults, aged 25 to 37 years. Arterial stiffness was measured from M-mode ultrasounds of common carotid artery using Peterson's (Ep) and Young's (YEM) elastic modulus. African Americans displayed a lower frequency of the T allele than did whites (0.131 v 0.321, P < .001). The T allele was associated with lower systolic BP in African Americans (P = .04) but not in whites. African Americans showed significantly higher values of Ep (that is, increased stiffness) than did whites (49.9 kPa vs 45.5 kPa, P = .003), whereas no such difference in ethnicity was found for YEM, a measure of elasticity adjusted for relative wall thickness. After controlling for sex, age, body mass index, insulin, heart rate, and mean arterial pressure, the T allele was associated with significantly lower values of Ep (P = .037) and YEM (P = .068) in African Americans. Although the genotype effect on Ep and YEM was not significant in whites, trends were similar to those in African Americans. In the total sample, including ethnicity as an additional covariate, the G894T genotype was significantly associated with Ep (P = .046) and YEM (P = .035). These results suggest that the allelic variation (G894T) of the eNOS gene or a locus closely linked to it is associated with lower arterial wall stiffness, adjusting for BP levels, in young adults. Am J Hypertens 2004;17:553-559 © 2004 American Journal of Hypertension, Ltd.