Population studies indicate that moderate hyperbilirubinemia is associated with reduced incidence of cardiovascular diseases including hypertension. Despite this correlative evidence, no studies have directly tested the hypothesis that moderate increases in plasma bilirubin levels can attenuate the development of hypertension. This hypothesis was tested by treating mice with Indinavir, a drug which competes with bilirubin for metabolism by UDP-Glucuronosyltransferase 1A1 (UGT1A1). Treatment of mice with Indinavir (500mg/kg/day, gavage) resulted in a two fold increase in plasma unconjugated bilirubin levels. Next, we determined the effect of Indinavir induced changes in plasma bilirubin on the development of angiotensin II (Ang II) dependent hypertension. Moderate hyperbilirubinemia was induced 3 days prior to the implantation of an osmotic minipump which delivered Ang II at a rate of 1 µg/kg/min. Ang II infusion increased mean arterial pressure (MAP) by 20 mmHg in control mice but by only 6 mmHg in mice treated with Indinavir (n=6). Similar to Indinavir treatment, direct infusion of bilirubin (37.2mg/kg/d intravenously) resulted in a two fold increase in plasma bilirubin levels and also attenuated the development of Ang II-dependent hypertension. Moderate hyperbilirubinemia resulted in an increase in plasma nitrate/nitrite levels which averaged 36 ± 2 vs. 50 ± 7µM in Ang II vehicle vs. Indinavir treated mice (n=5). Moderate hyperbilirubinemia resulted in attenuation of vascular oxidative stress as determined by dihydroethidium staining of aortic segments. These results indicate that moderate hyperbilirubinemia prevents Ang II dependent hypertension by a mechanism which may involve decreases in vascular oxidative stress.