Peripheral blood mononuclear cells, PBMC, from 64 HIV-1-infected patients were tested for natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) functions against HIV-1-infected U937 clone 2 cells. The ADCC function was tested both with serum and effector cells from the same patient, with an HIV-1 antibody positive serum and with rabbit IgG antibodies against beta 2-microglobulin expressed on the virus-infected target cells. NK and ADCC functions were often found to be suppressed in HIV-1-infected individuals regardless of the severity of HIV-1 infection. The fact that impaired effector cell functions could be detected even in asymptomatic carriers, suggests that profound changes in cellular immunity may be present at an early stage of HIV-1 infection.