The aim of this study was to investigate the association between urinary 90 kDa N-domain Angiotensin I-converting enzyme (ACE) form with C-reactive protein (CRP) and homocysteine plasma levels (Hcy), urinary nitric oxide (NOu), and endothelial function (EF) in normotensive subjects. Forty healthy subjects were evaluated through brachial Doppler US to test the response to reactive hyperemia and a panel of blood tests to determine CRP and Hcy levels, NOu, and urinary ACE. They were divided into groups according to the presence (ACE90+) or absence (ACE90-) of the 90 kDa ACE, the presence (FH+) or absence (FH-) of family history of hypertension, and the presence or absence of these two variables FH+/ACE90+ and FH-/ACE90-. We found an impaired endothelial dilatation in subjects who presented the 90 kDa N-domain ACE as follows: 11.4% ± 5.3% in ACE90+ compared with 17.6% ± 7.1% in ACE90-group and 12.4% ± 5.6% in FH+/ACE90+ compared with 17.7% ± 6.2% in FH-/ACE90-group, P < 0.05. Hcy and CRP levels were statistically significantly lower in FH+/ACE90+ than in FH-/ACE90-group, as follows: 10.0 ± 2.3 μM compared with 12.7 ± 1.5 μM, and 1.3 ± 1.8 mg/L compared with 3.6 ± 2.0 mg/L, respectively. A correlation between flowmediated dilatation (FMD) and CRP, Hcy, and NOu levels was not found. Our study suggests a reduction in the basal NO production confirmed by NOu analysis in subjects with the 90 kDa N-domain ACE isoform alone or associated with a family history of hypertension. Our data suggest that the presence of the 90 kDa N-domain ACE itself may have a negative impact on flowmediated dilatation stimulated by reactive hyperemia. Online address: http://www.molmed.org doi: 10.2119/2007-00112. Fernandes NO synthesis may be the first detectable evidence of endothelial dysfunction. ED is present in healthy normotensive subjects who are at high risk for the development of essential hypertension (18).Although there is a general agreement that endothelium-dependent vasodilatation is impaired in patients with essential hypertension, the relationship between this defect and plasma concentrations of nitric oxide is unclear (17).Most cardiovascular risk factors have been recognized to promote a proinflammatory state (19). Among them, arterial hypertension has been related to many circulating inflammatory markers such as C-reactive protein (CRP) and homocysteine (Hcy), (20)(21)(22) independently of other risk factors, promoting the idea of hypertension as a potentially pro-inflammatory condition (22). Studies have clearly established that CRP predicts a future risk of cardiovascular disease in apparently healthy people (23). The mechanism linking Hcy with cardiovascular disease may be the induction of vascular damage, although the exact mechanism is not understood fully. On the other hand, some prospective studies have shown only a weak or no relationship between homocysteine and cardiovascular disease (24).Our purpose is to test the hypothesis that the presence of the 90 kDa Ndomain ACE form in human urine could be associated with...