Fractions of complex glycosphingolipids were prepared from adult, cord, and i phenotype erythrocytes by the method elaborated for the isolation of poly(glycosy1)ceramides. In contrast to poly(glycosy1)ceramides which comprise on the average 30 glycosyl units and about 5 branching points, i.e. 3,6-di-O-substituted galactopyranosyl residues, per mole of glucose, complex glycosphingolipids from cord and i erythrocytes comprise 6 and 15 glycosyl units respectively and only 0.7 branching points. The latter substances exhibited also a high i activity which was not detected in poly(glycosy1)ceramides.Erythrocyte membranes were labeled with radioactive N-acetylgalactosamine (GalNAc) from UDP-GalNAc using a purified A-blood-group gene-specified transferase of GalNAc. It was found that electrophoretic mobilities in dodecylsulfate-gel electrophoresis of all glycoconjugates which accepted GalNAc were increased in i as compared to I membranes. We conclude that the absence of highly branched glycosphingolipids in cord and i erythrocytes as well as the reduction of apparent molecular weights of the glycoconjugates, which are substrates for A-gene-specified transferase of GalNAc, result from a single cause, that is an inadequacy of the biosynthetic process which is responsible for the formation of GlcNAcl + 6Gal structures.