Alterations in body fat distribution as well as serum lipid and glucose metabolism are increasingly being reported among HIV-infected individuals, particularly among those taking protease inhibitor (PI)-based therapy, now a standard of care in the treatment of HIV-infected patients. The etiology of these changes is unknown. We seek to undertake a prospective analysis of 30 antiretroviral naive HIV-invected patients, half of whom will be assigned to PI-based antiretroviral regimens while the other half will receive non-PI-based regimens. Extensive baseline diagnostic evaluations will be performed on all patients prior to the initiation of antriretroviral therapy and then approximately 6 months after the initiation of treatment. Metabolic studies will be perfomed at the General Clinical Research Center (GCRC). Baseline evaluations will examine body composition, basal hormone levels, and measures of insulin resistance. Participants will report fasting to the GCRC for a variety of tests to begin to define the mechanisms for fat redistribution, lipid, cortisol, and glucose metabolism including bioelectric impedance analysis, measures of resting energy expenditure, fasting lipid profile, measures of insulin sensitivity, free fatty acid levels, sex hormone levels, leptin levels, and examination of the hypothalamic-pituitary adrenal axis. It is hoped that the collected information will elucidate those metabolic changes occurring consequent to protease inhibitor use and will enable the development of a more specific hypothesis as to the mechanism by which fat maldistribution and insulin resistance take place in this population which can then be more broadly evaluated.