- Inclusion criteria for HIV infected children- a) The participants may be either antiretroviral treatment naive, or experienced. Those individuals who are experienced will be treated with at least one new drug in addition to the protease inhibitor. The selection of the new antiretroviral regimen will be directed by a review of the patient's previous drug treatment history and/or the genetic or phenotypic characteristics of the patient's virus; b) We will recruit subjects from all CDC categories. Disease severity will subsequently be analyzed as a covariate; c) There will be no height, weight or other anthropometric inclusion criterion (these factors will be analyzed as covariates); d) All subjects will be studied when they have not had an acute superinfection for at least four weeks.