During perfusion of an isotonic solution containing 56 mmol/l glucose and 122 mmol/l sodium chloride, net movements of water and sodium and glucose absorption were measured in the absence and presence of intraluminal hydrocortisone along 20-cm segments of proximal jejunum in five normal subjects and five patients with active coeliac disease. In normal subjects, the mean net absorption of water and sodium was significantly increased in the presence of hydrocortisone decreased. In the coeliac patients, the mean net secretion of water and sodium was significantly decreased. In neither group was the effect of hydrocortisone associated with a significant increase in glucose absorption. Similar changes in net movements of water and sodium occurred in both groups, even though absorption of hydrocortisone in coeliac patients was 44% of the control value. These results suggest that hydrocortisone may have exerted a local effect on the mucosal transport of water and sodium.