The two sulfated glucuronic acid containing glycolipids, sulfate-3-glucuronyl paragloboside (SGPG) and sulfate-3-glucuronyl lactosaminyl paragloboside (SGLPG), were prepared by ion exchange chromatography of lipid extracts from bovine cauda equina. Thin layer chromatography (TLC) immunostaining and an enzyme-linked immunosorbent assay (ELISA) were used to show that the SGPG/SGLPG fraction was free of crossreactive antigenic components such as gangliosides. The results obtained by ELISA demonstrate that sera of all patients were validated IgM monoclonal anti-myelin-associated glycoprotein (MAG) demyelinating neuropathy display high titer antibodies with high affinity type titration curves. These antibodies were absent from the sera of 16 patients with other neurological diseases and ten normal controls. ELISA with SGPG/SGLPG as an antigen appears to be a valuable and highly specific immunodiagnostic test for determining anti-MAG antibody titers in the sera of patients. The amount (approximately 0.4 mg) of SGPG/SGLPG partially purified from 10 g of fresh tissue is sufficient for the preparation of approximately 100 96-well plates for ELISA procedures.