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Introduction: Sepsis leads to a complex systemic response of cytokines (pro and anti- inflammatory) which may be further modulated by endothelial nitric oxide (NO). Pharmacologic manipulation of endothelial NO via L-arginine supplemention or inhibitors has provided inconsistent clinical data, referred to as the “arginine paradox”. Bioavailability of L-arginine is negatively impacted by metabolism of L-arginine in the liver, toxicity of parenteral L-arginine, and asymmetric dimethylarginine (ADMA) inhibition. . The ratio of concentrations of L-arginine and ADMA correlates with improved endothelial function and is an indicator of improved NO synthase activity. L-citrulline offers an indirect and better tolerated means of supplementing arginine and therefore improved NO availability. The goal of this study was to determine whether citrulline (CIT) supplementation altered the L-arginine/ADMA ratio in a rat sepsis model with varying degrees of severity.Methods: Sepsis was induced with 2 cecal ligation (CLP) models in Wistar rats. Citrulline supplementation was provided to half the animals as 8% citrulline supplemented feed for 3 weeks. Baseline L-arginine, ADMA, and citrulline were assessed followed by comparison of the following groups at day 0, 1, and 3: Sham operated; CLP 8mm (localized); and CLP 12mm (extensive). Blood was obtained via cardiac stick at the time of euthanasia. Measurements were performed with liquid chromatography and mass-spectrometry (LC/MS). Parametric 2 sample t-test and Mann Whitney U was used for statistical analysis with significance set at p<0.05Results: 98 Wistar rats were evaluated and survival was similar (85%) in both sepsis models with and without citrulline. The baseline L-arginine/ADMA ratio did not change significantly by the administration of CIT (113 vs. 164µmol/l, p=0.078). The ratio improved significantly on post-op day 1 and 3 in the CIT/Sham compared to non-citrulline group (104 vs. 222µmol/l , p=0.042 and 120 vs. 241µmol/l, p=0.004) and the same was seen in the CIT/CLP8 group (115 vs. 186µmol/l, p=0.048 and 72 vs.153, p=0.0180). There was no statistical difference in ratio between CIT/CLP12 and non-citrulline group on post-op day 1 and 3 (68 vs. 97µmol/l , p=0.055and 95 vs.112µmol/l, p=0.568).Conclusion: The data suggest that 3 week supplementation with citrulline does not alter the baseline L-arginine/ADMA ratios but does appear to improve both the response to sham laparotomy and localized sepsis. Citrulline may provide a safe means of modulating pathologic endothelial dysfunction. Further work is needed to confirm the results and mechanism of this effect.