Prednisolone absorption was studied in 13 normal subjects, eight patients with ulcerative colitis and 21 patients with Crohn's disease, by measuring plasma levels after a single oral dose. Absorption of the drug was delayed in all patient groups. The peak plasma level of the drug was lower in patients with extensive small bowel Crohn's disease. Patients in this category may need higher doses of oral prednisolone than other patients with inflammatory bowel disease.