Immunologic characteristics of intestinal mucosal lymphoid cells from patients with inflammatory bowel disease and controls have been compared. Mononuclear cells isolated by enzymatic means from intestinal tissues involved with inflammatory bowel disease were present in greater numbers, with increased proportions of macrophages and B-lymphocytes, particularly cells bearing intrinsic membrane immunoglobulin G. Synthesis of immunoglobulin G, measured by radioimmunoassay, was increased tenfold in inflammatory bowel disease, while immunoglobulin A synthesis per 10(6) cells was unchanged. "Null" or K-lymphocytes were absent from all populations, and antibody-dependent cellular cytotoxicity (a K-cell-mediated function) was not demonstrable. Taken together, the results fail to support a role for antibody-dependent cellular cytotoxicity or a defect in secretory immunoglobulin A, but rather focus attention upon possible forms of immunoglobulin G-mediated tissue damage in the pathogenesis or perpetuation of inflammatory bowel disease.