A variety of phenotypic abnormalities of peripheral blood lymphocytes from 8 HIV-carriers (HIVC), 6 patients with common variable immunodeficiency disease (CVID), and 13 patients with selective immunoglobulin deficiency (SIgD) were compared using two-color flow cytometry. There was a close resemblance in phenotypic abnormalities between HIVC and the patients with CVID; i.e., increases in CD8+CD11-, Leu7+CD16- and CD3+DR+ cells, and decreases in CD4+Leu8+, CD4+Leu8-, Leu7+CD16+ and Leu7-CD16+ cells. The increase in CD3+DR+ cells was due to an increase in CD8+DR+ cells. The CD4/CD8 ratio was inverted in both groups. A strong correlation coefficient (CC) was found only between the CD4/CD8 ratio and CD4+Leu8+ cells in HIVC, while CC was also high between the CD4/CD8 ratio and CD8+CD11- cells in CVID. The phenotypic abnormalities of the patients with SIgD were various and no significant difference was found against the control, except for an increase in CD4+Leu8+ cells and a decrease in CD4+Leu8- cells, which suggests heterogeneity of immunological deficits in this group. In severe immunodeficiency, ineffective killer cells appeared to be induced as a result of an adaptive change involved in recurrent or persistent viral infections, and Leu8 molecule may be concerned in the susceptibility of CD4+ cells to HIV.