1. The further purification of a polypeptide having potent enterogastrone activity, without CCK-PZ effects, is described.2. The material was inhibitory when doses of 1.0 mug/kg.hr were administered intravenously. Amino acid analyses demonstrated the absence of proline, a high content of glutamine and a preponderance of lysine over arginine. Tryptic degradation destroys the inhibitory effect of the polypeptide. Further studies must be performed before the physiological status of the polypeptide can be ascertained.