The effect of an intravenous bolus injection of cholecystokinin octapeptide (CCK-8; 0.85 micrograms/kg) on the release of cortisol, prolactin, vasopressin, and oxytocin was studied in sheep (n = 10). Concentrations of these hormones were measured in blood samples taken before (-10, 0 min) and after (5, 10, 20 min) administration of a saline vehicle or vehicle + CCK. Following CCK treatment, levels of cortisol were raised after 10 and 20 min, prolactin and vasopressin concentrations were increased after 5 min, and oxytocin secretion was unaffected.