The HNK-1 carbohydrate epitope, which is shared by several members of the immunoglobulin gene super-family, is also the target epitope for IgM anti-MAG autoantibodies in patients with demyelinating neuropathy. By Western blot analysis, there are 7 HNK-1 immunoreactive glycoproteins in human peripheral nerve myelin, two of which have previously been identified as the myelin associated glycoprotein (MAG) and the P0 glycoprotein. In this study, the remaining HNK-1 bearing glycoprotein bands were characterized by immunoblot and NH2-terminal sequence analysis, and were all identified as degradation products or aggregates of the Po glycoprotein. MAG and P0 are therefore the only HNK-1 bearing glycoproteins in human peripheral nerve myelin.