The isolation, primary structure and chemical synthesis of human peptide YY (PYY) are described. The peptide was purified from human colonic extracts using a chemical method which detected the C-terminal tyrosine amide structure of PYY. Human PYY consists of 36 amino acid residues and the complete amino acid sequence is: Tyr-Pro-Ile-Lys-Pro-Glu-Ala-Pro-Gly-Glu- Asp-Ala-Ser-Pro-Glu-Glu-Leu-Asn-Arg-Tyr-Tyr-Ala-Ser-Leu-Arg-His-Tyr-Leu- Asn-Leu-Val-Thr-Arg-Gln-Arg-Tyr-NH2. The differences between the structures of porcine and human PYY are at positions 3 (Ala/Ile replacement) and 18 (Ser/Asn). Synthetic human PYY prepared using a solid-phase synthetic technique was found to be structurally identical to the natural peptide.