The profound immune impairment that results from HIV-1 infection is due, at least in part, to the loss of CD4+ T cells and the cytokines these cells secrete, especially IL-2 and interferon-gamma. Antiretroviral agents do not directly address the problem of immune impairment. Replacement of IL-2 at nontoxic doses may prevent or delay clinical immunosuppression and its attendant opportunistic infections. Also, since patients with HIV-1 infection respond suboptimally to routine protein and polysaccharide immunizations, IL-2 may provide an adjuvant effect on vaccine responses.