Published studies suggest that sulfasalazine is effective in treating mild to moderate attacks of ulcerative colitis. Its usefulness in severe attacks has not been adequately tested. Published reports also justify the use of sulfasalazine to prevent recurrence of ulcerative colitis. It is not clear how long maintenance therapy should be continued, but evidence to date favors prolonged treatment in the absence of side effects. In treatment of Crohn's disease, sulfasalazine has been shown to be effective when disease involves the colon or the colon and small intestine. Maintenance therapy does not prevent relapse. Recent studies have indicated that 5-aminosalicylic acid (5-ASA) may be the therapeutic moiety of sulfasalazine, and sulfapyridine (SP) may be related to most of the side effects. Therefore, research is under way to develop a product that contains 5-ASA without the sulfonamide component and that is capable of reaching the colon without being absorbed in the upper small intestine.