This is a 48-week, observational study of lean body mass, appetite, functional performance, and systemic markers of inflammation during highly active antiretroviral therapy (HAART) in patients co-enrolled in ACTG antiretroviral studies. Patients are stratified by body mass index (BMI) into 2 cohorts: less than 23 kg/m2 versus greater than or equal to 23 to 28 kg/m2. At selected study visits, times of antiretroviral medication change, and following the diagnosis of an AIDS-defining event, the following are assessed: height (screening visit only), weight, lean body mass, appetite (by questionnaire), functional performance (by questionnaire), and markers of systemic inflammation.