Examining tissues outside the bloodstream in HIV-infected patients, patients with Idiopathic CD4 lymphopenia (ICL) and, for comparison, HIV-uninfected healthy volunteers (hereafter referred to as healthy volunteers), can provide insights into the pathogenesis of HIV infection and ICL. This protocol will provide a mechanism for sampling tissue sites. A total of 430 HIV-infected patients, 100 ICL patients and 105 healthy volunteers will be enrolled in these studies. To assess changes in viral load and immunological parameters at sites outside the bloodstream during therapy of HIV-infected patients, sequential tonsillar, lymph node, or intestinal biopsies, or bronchoscopy with bronchoalveolar lavage (BAL) will be undertaken during the course of therapy. In a small number of patients, sequential or simultaneous lymph node biopsies will be performed. In addition, uninfected healthy volunteers will be enrolled to have a tonsillar or intestinal biopsy, or bronchoscopy with BAL; this will allow comparison of immunologic parameters in HIVinfected and uninfected tonsillar or intestinal tissues, or BAL fluid. Finally, ICL patients may have tissue sampling to assess lymphocyte distribution and possible function in tissues to better understand the pathogenesis of their lymphopenia. Sequential or simultaneous tissue sampling may occur and longitudinal samples may also be obtained to assess stability in tissue compartments or effect of possible immunomodulatory treatments.