KB and HEp-2 are cell lines that are commonly used for autoantibody detection. We have used conventionally produced and monoclonal antibodies as probes for cytoskeletal antigens in these cells. The presence and distribution of microfilament, microtubule, and intermediate filament antigens (vimentin and keratin) have been established. We have also confirmed that anti-vimentin antibodies of one clone do crossreact with DNA on an immunoadsorbent column, although this antibody did not appreciably stain the nucleus of either cell type.