The long-term efficacy of combination antiretroviral therapy may relate to augmentation of anti-human immunodeficiency virus type 1 (HIV-1) CD8⁺ T-cell responses. We found that prolonged treatment of late-stage HIV-1-infected patients with a protease inhibitor and two nucleoside reverse transcriptase inhibitors failed to restore sustained, high levels of HIV-1-specific, HLA class I-restricted, cytotoxic-T-lymphocyte precursors and gamma interferon (IFN-γ) production by CD8⁺ T cells. In some patients, particularly those initiating three-drug combination therapy simultaneously rather than sequentially, there were early, transient increases in the frequency of anti-HIV-1 CD8⁺ T cells that correlated with decreases in HIV-1 RNA and increases in T-cell counts. In the other patients, HIV-1-specific T-cell functions either failed to increase or declined from baseline during triple-drug therapy, even though some of these patients showed suppression of plasma HIV-1 RNA. These effects of combination therapy were not unique to HIV-1 specific T-cell responses, since similar effects were noted for CD8⁺T cells specific for the cytomegalovirus pp65 matrix protein. The level and breadth of CD8⁺ cell reactivity to HLA A*02 HIV-1 epitopes, as determined by IFN-γ production and HLA tetramer staining after combination therapy, were related to the corresponding responses prior to treatment. There was, however, a stable, residual population of potentially immunocompetent HIV-1-specific T cells remaining after therapy, as shown by tetramer staining of CD8⁺CD45RO⁺ cells. These results indicate that new strategies will be needed to target residual, immunocompetent HIV-1-specific CD8⁺ T cells to enhance the effectiveness of antiretroviral therapy in patients with advanced immunodeficiency.