Mesalazine 4g Once Daily Versus 4g in Two Divided Doses in Active Ulcerative Colitis.

Inclusion Criteria: Patients will be included if they comply with the following inclusion criteria determined at baseline, prior to first drug administration: * Aged over 18 years. * Newly diagnosed or relapsing mild to moderate ulcerative colitis with disease extension beyond rectum (of at least 12-18 cm from the anorectal junction). All patients must have had at least one total colonoscopy in their disease history (within the previous 5 years). * Disease activity will be assessed on the 15 days before inclusion and according to ulcerative colitis disease activity index (UC-DAI) score. The UC-DAI score will be from 3 to 8 (mild: 3-5 or moderate: 6-8). * Men or non pregnant women. * Women with childbearing potential must be using a contraceptive method judged effective by the investigator. * Oral maintenance treatment with azathioprine or 6-mercaptopurine (taken for at least 6 months at stable dose and continued at the same dose throughout the study) is permitted. * Informed consent given. Exclusion Criteria: The patients will not be included in the study if one of the following exclusion criteria is fulfilled at baseline, prior to first drug administration: * Proctitis (less than 12-18 cm from the anorectal junction). * Previous colonic surgery. * Previously failed to respond to steroids within the previous year. * Non-response to rectal 5-Amino Salicylic Acid (5-ASA) therapy or to oral 5-ASA therapy at a dose \> 3g/day for induction of remission within the previous year. * Current relapse lasting more than 6 weeks (for patient recently diagnosed the period of 6 weeks runs from the endoscopic diagnosis)(from what patient says). * Severe/fulminant ulcerative colitis. * Evidence of other forms of inflammatory bowel disease or infectious disease. * Allergy to aspirin or salicylate derivatives. * The following treatment will be forbidden during the study (if present at selection, a wash-out will be necessary): * Loperamide and other antidiarrheal agents, mucilages, antibiotics: 1 week wash-out. * Oral steroids: 4 weeks wash-out. * Rectal steroids: 2 weeks wash-out * Repeated treatment (\> 3days of use) of non steroidal anti-inflammatory drugs (NSAID) oral or rectal route: 1 week wash-out (aspirin ≤ 325 mg/day used for cardioprotection is allowed). * Sulfasalazine \> 4g/day or mesalazine or 4-ASA at a higher dose than what is permitted in the local formulary or standard care for maintenance treatment: 4 weeks wash-out * Immunomodulating/suppressing drugs: 3 month for wash out (except for patients maintained on azathioprine or 6-mercaptopurine -see above). * Known significant hepatic or renal function abnormalities. * Moderate/severe abnormal renal, hepatic or blood count tests defined as: creatinine plasma value \> 1.5 x Upper Limit of Normal (ULN) or white blood cells \< 3500/mm˄3 or \> 15000/mm˄3 or Platelets \< 100000/mm˄3 or \> 800000/mm˄3 or aspartate aminotransferase/alanine Aminotransferase (ASAT/ALAT) \> 3 x ULN or Gamma glutamyl transpeptidase (GGT)/Alkaline Phosphatase's \> 3 x ULN (Primary Sclerosing Cholangitis is not an exclusion criteria). * History or physical examination findings indicative of active alcohol or drug abuse, * Pregnancy or breast-feeding, * History of disease, including mental/emotional disorder, that might interfere with their participation in the study, * Participation in another clinical study in the last 3 months. * Inability to comply with the protocol requirements. * Inability to fill in the diary cards.