Motowo Tomita, 1 Heinz Furthmayr,* and Vincent T. Marchesi abstract: Peptides of glycophorin AMN were prepared by cyanogen bromide cleavage and by chymotryptic and tryptic digestion. Cyanogen bromide cleavage produces three frag-ments which account for the entire polypeptide chain. Trypsin and chymotrypsin cleave completely at several sites, but incompletely at sites within the glycosylated segment of the polypeptide chain. Some of the latter sites become accessible to proteolysis after desialation in addition to exposure of new sites for cleavage. The amino acid sequence of glycophorin AMN has been determined by manual Edman degradation, using both the direct Edman and the dansyl-Edman procedures simultaneouslyfor determination of glycosylated amino acid residues. The automated procedure was used for sequence determination of a hydrophobic peptide. Glycophorin A is a polypeptide chain of 131 amino acid residues and contains 16 oligosaccharide units attached to the amino-terminal third of