Bilirubin may have a major role in the prevention of cardiovascular disease based on recent data regarding its anti-oxidant properties. We determined the relationship between total serum bilirubin and vascular reactivity in a large cohort of individuals with diabetes, a disease associated with known oxidant stress. We studied 302 individuals: 52 controls, 37 with type 1 diabetes, 213 with type 2 diabetes. Highresolution ultrasound was used to measure flow-mediated dilation (FMD; endotheliumdependent) and nitroglycerin-induced dilation (NID, endothelium-independent) of the brachial artery. Laser Doppler perfusion imaging was used to measure microvascular reactivity in the forearm skin before and after iontophoresis of acetylcholine (endothelium-dependent) and sodium nitroprusside (endothelium-independent). Bilirubin levels were higher in the type 2 diabetes group (0.71 ± 0.34 mg/dl) compared to controls (0.56 ± 0.26 mg/dl, p < 0.0001). A weak inverse correlation was observed between bilirubin and FMD (r = -0.125, p = 0.032) and skin endothelium-dependent vasodilation (r = -0.157, p = 0.019). In multivariate analyses, however, these correlations were not statistically significant. There is no association between bilirubin levels and vascular reactivity in the macro- and microcirculation of individuals with diabetes. Bilirubin, therefore, does not correlate with predictors of cardiovascular risk in the diabetic population. [ABSTRACT FROM AUTHOR]