The ultimate consequence of infection with HIV is profound immunosuppression that is the result of both quantitative and qualitative abnormalities of the helper/inducer subset of T lymphocytes. The initial pathogenic event in HIV infection is binding of the envelope glycoprotein of HIV to the CD4 receptor molecule present on the surface of CD4+ T lymphocytes and monocyte/macrophages. In vivo the reservoir for HIV infection in the peripheral blood is the CD4+ T cell, whereas in other tissues the monocyte/macrophage may play a substantial role. As disease progresses in HIV-infected individuals, the viral burden in the peripheral blood CD4+ T cells increases. An understanding of the mechanisms involved in the transition from an initially low viral burden during the asymptomatic phase of HIV infection to the higher levels of virus expression detected in late stage disease is being investigated intensively. A number of potential agents that may influence regulation of HIV expression have been identified includ...