Abstract: A polypeptide having important biological activity including systemic vasodilation, hypotension, increased cardiac output and bronchodilation is isolated from intestines of chickens. The isolation procedure for purification includes extraction, ion-exchange chromatography, gel chromatography and countercurrent distribution separation. The polypeptide has the general amino acid structure:His-Ser-Asp-Ala-Val-Phe-Thr-Asp-Asn-Tyr-Ser-Arg-Phe-Arg-Lys-Gln-Met-Ala-Val -Lys-Lys-Tyr-Leu-Asn-Ser-Val-Leu-Thr-NH.sub.2. Therapeutic biological actions may be produced in animals and humans by administration of 0.02-10 .mu.g of the peptide per kg of body weight.