The aim of this proposal is to identify the early nutritional and metabolic changes which occur in HIV-infected children using new, non-invasive methods for the assessment of protein and energy metabolism and body composition. We will measure, in HIV-infected children with and without poor growth, and in age matched HIV-uninfected children: 1) whole-body protein turnover using the N-glycine end product technique; 2) energy expenditure and its relationship with dietary energy intake and expenditure and its relationship with dietary energy intake and body composition; and 3) body composition and body water distribution, using conductance spectroscopy and D2O dilation.