BACKGROUND Luminal anionic sulphide may contribute to epithelial damage in ulcerative colitis. Thiol methyltransferase (TMT) governs sulphide detoxification by the colonic mucosa and circulating erythrocytes.

AIMS To measure levels of TMT activity in erythrocytes of surgically treated cases of colitis or in rectal biopsies of defined groups of colitis.

PATIENTS Venepuncture blood was obtained from 37 blood donors and 27 subjects who had previously undergone a proctocolectomy for colitis: 18 for ulcerative colitis and nine for Crohn's colitis. Rectal biopsies from 122 cases were obtained: 47 without mucosal disease, 33 post-colon resection for cancer, 14 with moderate to severe ulcerative colitis, 15 with quiescent ulcerative colitis, seven with acute Crohn's colitis, and six with radiation proctitis.

RESULTS Erythrocyte TMT activity of surgically treated cases of colitis was significantly elevated (p<0.001) compared with control cases. TMT activity of rectal biopsies was significantly decreased (p<0.02) in acute but not quiescent ulcerative colitis, Crohn's colitis, or radiation colitis.

CONCLUSIONS Erythrocyte TMT activity was persistently elevated after proctocolectomy for Crohn's disease and ulcerative colitis. No primary defect of TMT activity was found in any case of unoperated colitis but mucosal activity was diminished with disease progression of ulcerative colitis. Studies of genetic control of TMT activity of erythrocytes in inflammatory bowel disease appear worthwhile.