Over the past five years, we have been successfully able to prospectively collect growth and nutrition data on over 100 HIV-infected and control children. We have determined changes in growth, body composition, energy utilization, cytokine production, and effective nutritional intervention programs for these children. In this competing renewal will continue to collect data on growth, body composition, dietary intake, and energy utilization on this unique cohort of HIV-infected children. As the face of pediatric HIV is every changing, capture and continued assessment and follow-up of these children with very early preceding the advent of newer therapeutic regimens is invaluable. We will quantitate protein metabolism through whole body protein turnover studies using 13C leucine in the clinical spectrum of HIV in children (CDC class A,B,C, and controls), knowing that there are significant declines in lean body mass in these children over time. We will determine if there are associations between protein turnover, viral activity, and other infectious outcomes. As well, with the advent of protease inhibitors (PIs) and other highly active anti-retroviral therapies (HAART), changes in body composition and improved clinical outcomes are apparent. We will quantitate and characterize these changes through body composition studies that study regionalization of fat distribution and follow changes longitudinally and with new therapies. We will also determine if abnormal glucose metabolism is apparent in these children and may potentially led to the fat redistribution syndrome. Lastly practical interventions to increase lean body mass and function through exercise programs are proposed and are unique both to HIV, as well as pediatrics in general. We will determine if a 12 week exercise regimen, with reinforcement of outside activities are effective in improving lean body mass, strength, endurance, flexibility, and functional status in HIV-infected children while comparing them to an "attention" control group.