The therapeutic effect of sucralfate on ulcerated gastric and duodenal mucosa is well known. There is, however, almost no information about its activity in colitis. Experimental colitis was produced in rats by rectal instillation of 1 ml of 10 percent acetic acid, and 1.5 ml of a 20 percent suspension of sucralfate was then administered every 12 hours for various lengths of time. Study animals and appropriate controls were killed after 3, 7, 10, or 14 days. The distal colons were studied macroscopically and histologically. Colonic prostaglandin E2 levels were measured in animals killed after 3, 7, 10, or 14 days. The macroscopic score was significantly improved 10 and 14 days after induction of colitis, although the histologic appearance was unchanged. Acetic acid administration increased and sucralfate treatment reduced prostaglandin E2 levels in colitic animals on days 3 and 7, but not later. The present study supports a role for sucralfate in the treatment of colitis, but further studies on the mechanism of its effect and on its clinical activity are indicated.