The aminoethylated beta polypeptide chain of AII component from chicken hemoglobin was digested with pepsin [EC 3.4.23.1] and the resulting peptides were separated and purified by gel filtration, ion exchange chromatography, and paper chromatography. The amino acid composition and partial sequence of the peptic peptides were studied. From the results thus obtained, the primary structure of the beta polypeptide chain was established, taking account of the amino acid sequences of the tryptic peptides previously reported.