Reducing the dosing rate to a single daily dose for 8 weeks constitutes a simple method of improving treatment compliance but it is necessary to demonstrate at least equivalent efficacy compared to the twice daily dosing which is the reference regimen. This study was designed to show that mesalazine 4g once daily is at least as effective as mesalazine 4g in two divided doses per day in patients with mild to moderate ulcerative colitis after 8 weeks of treatment with a better compliance. To improve remission, both groups received an enema during the first 4 weeks, as usually done in current practice.