The presence of anti-colon antibody in the sera from patients with ulcerative colitis was demonstrated by antibody-dependent cell-mediated cytotoxicity (ADCC) assay. In addition, the high prevalence of lymphocytophilic antibody in the sera from patients with ulcerative colitis was obtained by fluorescence activated cell sorter (FACS) analysis. This lymphocytophilic antibody was absorbed by rat colon epithelial cells. Moreover the lymphocytes from ulcerative colitis showed lower binding capacity to this antibody, but acquired higher binding capacity after 20 hr incubation at 37 degrees C in vitro. These data suggest that ADCC may have some role in the pathogenesis of ulcerative colitis.