Three different bile acids--deoxycholic acid, chenodeoxycholic acid and ursodeoxycholic acid--were tested for their capacity to stimulate the adenylate cyclase in human colonic mucosa. This enzyme system was found to be sensitive towards vasoactive intestinal polypeptide and prostaglandin E2. These three bile acids were ineffective in activating the human cyclase system over a wide concentration range tested. Concentrations above 1 X 10(-5) mmol/l induced a dose-dependent inhibition of basal enzyme activity. These results suggest that bile-acid induced diarrhoea is not associated with activation of the membrane-bound adenylate cyclase system at least in man.