Eight patients with active ulcerative colitis (UC), refractory to usual combination medical therapy, were treated with a single i.v. dose of chimeric monoclonal antibody to recombinant human tumor necrosis factor alpha; many of these patients were scheduled for surgical colectomy because of their active disease. All patients responded extremely well to a single 5 mg/kg infusion of infliximab, with marked improvement after the infusion clinically, colonoscopically, and histologically on colonic biopsy. There were no significant complications or side effects; mean duration of remission has not been determined because none of the patients have relapsed. Infliximab appears to be a potent agent for inducing remission in refractory patients with ulcerative colitis.