The effects of C-terminal unsulfated cholecystokinin octapeptide (CCK-8US) and its fragments C-terminal heptapeptide (CCK-7), C-terminal hexapeptide (CCK-6) and C-terminal pentapeptide (CCK-5) were studied on the arterial blood pressure and the isolated rat heart. CCK-8US had only slight hypertensive and no cardiac effects. CCK-5, CCK-6 and CCK-7 had no effect on the arterial blood pressure, the cardiac contraction amplitude and the heart rate. Only CCK-7 increased coronary outflow of the isolated rat heart. CCK-8US and C-terminal fragments; CCK-7 have little effect on the circulation of the rat.