The complete amino acid sequence of P2 protein from human peripheral nerve myelin was determined from nine staphylococcal protease peptides and four cyanogen bromide peptides. Human P2 protein is composed of 131 amino acids and has a molecular weight of 14,818. Compared to bovine P2 protein, there are replacements at nine positions (human in equilibrium bovine): 18(Asp in equilibrium Glu), 39(Thr in equilibrium Arg), 56(Thr in equilibrium Pro), 83(Ile in equilibrium Thr), 87(Gln in equilibrium Ala), 96(Arg in equilibrium Lys), 100(Lys in equilibrium Asn), 115(Ala in equilibrium Val), and 121(Gly in equilibrium Asp).