Using cultured skin shavings, human cellular cytotoxicity to uninfected and herpes simplex virus (HSV)-infected autologous and allogeneic fibroblasts and Chang liver cells was analysed in a 51Cr release assay. The effector cell requirements and characterization, time kinetics and antibody requirements were similar using each HSV-infected target cell in an antibody-dependent cellular cytotoxicity (ADCC) system. There was lower natural killer cytotoxicity (NKC) to uninfected autologous cells than unrelated cells in an 18 hr assay. NKC to infected autologous and unrelated fibroblasts was similar to that mediated against Chang liver cells. Thus NKC to uninfected fibroblasts correlated with the relationship of effector and target cells while NKC to infected cells correlated with the intrinsic lytic potential of the effector cells. The autologous system offers little advantage in the analysis of ADCC or NKC in normal individuals to virus-infected cells, but is probably crucial for the detection of HLA-restricted T-cell cytotoxicity. The demonstration of autologous anti-viral ADCC and NKC lends further credence to the in vivo importance of the mechanisms.