 In this study we propose to study lactate metabolism among persons with chronic HIV infection both on treatment and treatment naive and compare the results to uninfected control population. We will also study a subset of HIV infected persons with known underlying liver disease. Two methodologies will be used: a lactate challenge test and a forearm ischemia test. The effect of supplementation with cofactors which may have a positive effect on lactate metabolism by facilitating mitochondrial function will be studied as well. All persons enrolled for evaluation will have these tests repeated 4-6 weeks after supplementation with standardized doses of cofactors thiamine and L-carnitine between tests. Fat tissue samples and PBMCs will be collected and analyzed for quantity and function, and participants will have liver ultrasounds. Liver biopsies will be completed on those subjects where clinically indicated. The results of the study will provide important insights into the effects on lactate metabolism, nucleoside analogues, and HIV itself. 