To evaluate the safety and efficacy on clinical symptoms, mucosal histology and endoscopic mucosal appearance of two doses of SR140333B against placebo in patients with mild to moderate ulcerative colitis resistant to treatment with 5-ASA.

Patients with active mild to moderate ulcerative colitis that has not responded to a minimum of 4 weeks of 5-ASA will be randomized to receive single daily doses of either placebo, 600 mg SR140333B or 1800 mg of SR140333B for eight weeks. Patients will undergo baseline and end of study sigmoidoscopic assessments and complete daily symptom diaries during the study. Ulcerative colitis disease activity will be measured by both the overall and component subscores of the Mayo Disease Activity Index.

Inclusion Criteria:

• Age at least 18 years
• Ulcerative colitis of at least 6 months duration
• Patient's ulcerative colitis should remain active while taking 5-ASA or sulfasalazine for at least 4 week
• If taking corticosteroids, dose must be stable for at least 2 weeks prior to enrollment and not exceed 20 mg per day (prednisolone equivalent)

Exclusion Criteria:

• Crohn's disease
• Colonic dysplasia
• Stool culture positive for enteric pathogens
• Concurrent cancer or unstable medical condition
• Recent treatment with monoclonal antibody
• Recent introduction of thiazolidinedione
• Recent treatment with methotrexate or cyclosporine
• Recent treatment with an antibiotic prescribed for ulcerative colitis