Intravenous ciclosporin 4 mg/kg daily is rapidly effective as a salvage therapy for patients with refractory colitis, who would otherwise face colectomy, but its use is controversial because of risk of toxicity, and long-term failure rate. Opportunistic infections remain a serious concern, with a number of reports of death related to ciclosporin. Renal and neurotoxicity are also well-recognized. The drug should not be continued for more than 3-6 months and its main role is as a bridge to azathioprine or 6-mercaptopurine. Risks of toxicity can be reduced by using lower doses (2 mg/kg/day intravenously), by oral microemulsion ciclosporin, or by monotherapy without corticosteroids. Preliminary evidence shows good response rates, but further studies are needed to confirm optimal use of this potent, but hazardous, therapy.