In a selected group of human immunodeficiency virus (HIV)-infected patients we confirm the expansion of a CD8+ T-lymphocyte subset, i.e., the CD8+/Leu7+ cells, which account for 30% of the lymphocytes, compared to 3% in the control donors. In addition, a CD8+ T-lymphocyte subset that coexpresses class II (DR) antigens, i.e., CD8+/DR+ cells, is also increased from 1.5% in controls to 27% in the HIV-infected patients. Using three-color immunofluorescence and flow cytometry we can demonstrate that the CD8+/Leu7+ and the CD8+/class II+ cells are not distinct but overlapping subsets. In the HIV-infected patients 42% of the CD8+/Leu7+ cells were strongly positive for class II and these CD8+/Leu7+/class II+ cells accounted for 13% of all lymphocytes. These findings indicate that the expanded CD8+/Leu7+ cells are activated and hence might be actively involved in immune defense in acquired immune deficiency syndrome (AIDS).