Stress and depression are associated with more rapid loss of CD4 cells in HIV infection. Interventions that slow the advance of HIV infection and delay the introduction of antiretroviral therapy (ART) could make an important contribution to HIV management in both the developed and developing world. We are conducting a 330 person randomized, controlled clinical trial of MBSR for persons with HIV-1 infection and CD4 T-lymphocyte counts > 250 cells/µm who are not on antiretroviral therapy. Participants are randomized in a 1:1 distribution to either the MBSR intervention or to an education group that will control for the attention and social interaction aspects of MBSR. Participants are evaluated at 0, 3, 6 and 12 months. Key outcome measures at 12 months include differences in CD4 T cell counts, HIV viral load, perceived stress, depression, and positive affect. We are also examining whether MBSR is associated with changes in neuroendocrine function (autonomic nervous system activity, cortisol secretion) and alterations in immune function that may serve as intermediate steps between the neuroendocrine effects of MBSR and CD4 T cell counts, such as changes in T cell activation. A subset of 90 participants will be studied in additional detail using a structured laboratory stress challenge.