Histologic similarity of murine colonic graft-versus-host disease (GVHD) to human colonic GVHD and inflammatory bowel disease. In a study designed to determine which T-cell subsets are involved in the development of murine graft-versus-host disease (GVHD), a prospective histologic analysis of gastrointestinal involvement was performed. In C57BL/6JXDBA/2F1 (B6D2F1) recipients of DBA/2 donor spleen and bone marrow cells, the colonic histologic findings were found to be similar in many respects to the histologic findings reported in human colonic GVHD and were much more severe and diffuse than were the abnormalities of the small intestine. Host irradiation before transplantation was found to play an additive or synergistic role in the development of GVHD. Furthermore the histologic features noted in DBA/2----B6D2F1 murine colonic GVHD suggest that bone marrow and spleen cell transplantation in this strain combination may be a useful model for studying the immunologic mechanisms involved in human inflammatory bowel disease. Thus severe colonic disease noted during the course of DBA/2----B6D2F1 murine GVHD was found to have significant histopathologic similarities to both human GVHD enteropathy and other inflammatory diseases of the human colon. 