In a double-blind randomized clinical trial 18 patients with exacerbations of distal ulcerative colitis were treated for 4 weeks with enemas containing either prednisolone 21-phosphate 30 mg (PP) or beclomethasone dipropionate 1 mg (BDP) a surface-active corticosteroid. All 8 patients treated with PP showed clinical and endoscopic improvement in contrast with only 4 of 10 patients treated with BDP. Endocrinologic evaluation showed a significant decrease in morning plasma cortisol, in cortisol increase after synacthen, and in urinary free cortisol excretion after PP therapy, but no changes in these variables after BDP therapy. We conclude that PP enemas are more active in the treatment of ulcerative proctitis, but they cause a suppression of the adrenal cortex, in contrast to BDP.