This study is a prospective clinical study to evaluate the safety and efficacy of two different doses of Asacol for the treatment of moderately active ulcerative colitis. In addition, a new tablet formulation will be evaluated at one of the two doses.

• Drug: Asacol (mesalamine)
• Drug: asacol 400 mg (mesalamine)

• Active Comparator: Asacol (2.4 g/day)
• Experimental: Asacol (800 mg/day)

Inclusion Criteria:

• male or female between 18 and 75 years of age;
• have a confirmed diagnosis of ulcerative colitis with the extent varying from proctitis to pancolitis;
• currently demonstrating moderately active disease

Exclusion Criteria:

Patients will be excluded from admission to the study if they have/are:

• a history of allergy or hypersensitivity to salicylates or aminosalicylates;
• a history of extensive small bowel resection (>1/2 the length of the small intestine) causing short bowel syndrome;
• current renal or hepatic disease;
• participated in any drug or device clinical study within 30 days of entry;
• currently enrolled in any other clinical study;
• received any oral, intravenous, intramuscular, or rectally administered corticosteroids within 1 month prior to the Baseline Visit;
• received any other topical rectal therapy during the week prior to the Screening Visit;
• received immunomodulatory therapy including, but not limited to, 6-mercaptopurine, azathioprine, cyclosporine, or methotrexate within 3 months prior to the Baseline Visit;
• received a dose of mesalamine-containing compound by any route from which more than 1.6 g/day of mesalamine was available within 1 week prior to the Screening Visit (NOTE: 4 g/day of sulfasalazine and 4.5 g/day of balsalazide are equivalent to 1.6 g/day of mesalamine);
• received antibiotics, other than topical antibiotics, within 1 week prior to the Screening Visit;
• received aspirin (except for cardioprotective reasons up to a maximum dose of 325 mg/day) or NSAIDs within 1 week prior to the Baseline Visit;
• if female, positive pregancy test, or lactating.