The influence of cholecystokinin-octapeptide on the bioelectrical features of gastro-intestinal motility in sea-water fish (plaice) was investigated in chronic experiments. I. v. or intracerebral application of the peptide led to inhibition of the stomach cardia motor activity, to intensification and sparsity of the tonic and peristaltic contractions of the stomach pyloric part, and to an increase in the intestine fore-part activity. Vagotomy prevented the effect of intracerebral application of cholecystokinin. Atropine prevented this effect of cholecystokinin irrespective of the mode of its application. Phentolamine or propranolol did not alter the effect.