We investigated Epstein-Barr virus (EBV)-specific T cell responses in homosexual men with, and at risk for, AIDS. We studied healthy laboratory workers, healthy homosexual men, and patients with AIDS-related complex or AIDS. The cytotoxic activity, absolute number of T4 lymphocytes, and interleukin-2 (IL-2) production decreased, whereas the relative number of Ia+ lymphocytes increased with the extent of infection with the human immunodeficiency virus (HIV). Cytotoxic activity correlated positively with the number of T4 lymphocytes (r = .56, P less than .001) and the amount of IL-2 produced (r = .47, P less than .01) but not with interferon production. Recombinant IL-2, but not gamma interferon, could restore cytotoxic T cell activity to control levels in patients with early HIV infection. EBV-specific serological studies paralleled the T lymphocyte investigations. The increased EBV activity observed in progressive HIV infection may be related to a diminution in the auto-reactive population of the T4 lymphocyte subset and may be amenable to IL-2 reconstitution.