SUMMARYBackground: The optimal modalities of treatment with oral microemulsion ciclosporin in patients with severe, steroid-refractory ulcerative colitis are uncertain. Aim: To assess the applicability, in terms of efficacy and tolerability, of a standard oral microemulsion ciclosporin treatment protocol targeting relatively low blood ciclosporin concentrations, in patients with severe, steroid-resistant ulcerative colitis. Patients and methods: Patients with a severe attack of ulcerative colitis and no satisfactory response to intravenous corticosteroids were started on oral microemulsion ciclosporin. Dosages were adapted according to a standard protocol, targeting a blood predose ciclosporin concentration (C 0 ) of 100-200 ng/mL. Patients with-