CD8+ cytotoxic T lymphocytes (CTLs) in human immunodeficiency virus (HIV) patients have defects in cytolytic ability and proliferative potential. The surface receptor CD28 is important in regulating antigen-specific responses of T cells. We hypothesized that activated CD8+ CTLs in HIV patients would have altered expression of CD28. We examined surface expression of D44, a CD8+ CTL marker, and of CD28 on T cells from blood and bronchoalveolar lavage from HIV+ patients and normal volunteers. We found no significant difference between normal volunteers and HIV+ individuals in percentage of CD8 + D44+ CTLs in blood or the lung. In contrast, CD8+ CD28- T cells in the blood of HIV patients constituted 74% of CD8+ cells compared to 25% in normal subjects (p = 0.001), findings exaggerated in both normal and HIV+ lung. CD4 + CD28- blood T cells were significantly increased in HIV+ patients compared to normal subjects (24 vs. 1.5%, p = 0.004). The HIV infection itself did not directly downmodulate CD28 expression, demonstrated in the CD28+ SUPT1 cell line. Increased numbers of CD28- T cells may be the result of immunologic activation or of expansion of a preexisting CD28 subset. These findings have immunologie consequences for the antigen-specific response of T cells in HIV+ patients.