Serum prednisolone levels have been measured following the oral administration of 20 mg prednisolone in 10 normal subjects, in 9 patients with Crohn’s disease and in 6 with coeliac disease. Serum prednisolone levels showed more variation in patients with Crohn’s disease when compared to normal subjects. In those patients with Crohn’s disease who failed to respond to corticosteroid therapy, adequate serum levels of prednisolone were achieved. Patients with coeliac disease had levels similar to normal. Serum protein binding of prednisolone was not significantly different between the groups. We conclude that, even in the presence of mucosal damage, patients with coeliac disease and Crohn’s disease achieve therapeutic serum prednisolone levels.