The invention relates to carbohydrate ligands presenting the minimal Human Natural Killer-1 (HNK-1) epitope that bind to anti-MAG (myelin-associated glycoprotein) IgM antibodies, and their use in diagnosis as well as for the treatment of anti-MAG neuropathy. In particular, the invention relates to disaccharides of formula (I) and (II) wherein Z is optionally substituted phenyl, heteroaryl, arylcarbonyl, or heteroarylmethyl, and to therapeutically acceptable polymers comprising a multitude of substituents of formula (I) and/or formula (II), wherein Z is a bifunctional linker connecting the disaccharides to the polymer backbone.