Five patients with chronic continuous Crohn's colitis were treated with peroral Cyclosporin A (CyA) for 3 months in an open, uncontrolled pilot trial. The CyA dose was 10 mg kg-1 d-1 the first month of study, and thereafter 5 mg kg-1 d-1. Three of the patients initially showed some response to the treatment with decreases in the Crohn's disease activity index, but subsequently deteriorated. In one patient the condition was unchanged and another clearly worsened. Increases in serum creatinine levels were noted in three patients, and all of these also had decreased 51Cr-EDTA clearance indicating impaired renal function. Hypertrichosis and hyperaesthesia were also noted as side-effects. This study does not support the use of CyA in the short-term treatment of Crohn's disease in the colon.