Thirty-four patients with chronic inflammatory bowel disease, 23 with ulcerative colitis, and 11 with crohn's disease, weretreated with elemental diet. thirty-one patients had been on high dose prednisonetherapy one to four weeks prior to the diet with no or insufficient response. Fifteen patients (44%) went into remission when elemental diet was introduced as the only change of treatment. Furthermore six patients (18%) went into remission when the dietary treatment was supplemented with high dose prednisone treatment (2 cases) or an increase of prednisone dose (4 cases). Remission occurred in 16 of 21 patients with disease of moderate activity, but in only 5 of 13 cases with severe disease. Remission rate was higher in patients with a limited extent of the lesion, but 8 patients with extensive colitis responded to treatment. There was no significant change of haemoglobin serum iron, transferrin, albumin, orosomucoid, or renal excretion of creatinine. However, significant decreases were observed of sedimentation rate, renal urea excretion, faecal volume and daily number of bowel movements. Colectomy was performed in 8 patients whose condition remained unchanged or aggravated during treatment. Follow-up studies of non-operated patients who went into remission showed that 6 of 13 patients with ulcerative colitis were perfectly well 7-28 months after the study, 3 patients suffered a mild recurrence after 4-24 months, and 4 patients were colectomized 5-10 months later due to severe attack. Of 8 patients with Crohn's disease 4 remained unoperated and free of symptoms 22-35 months after the study.