The binding patterns of electrophoresed polypeptides from homogenates of human frontal lobe, cerebellum, and spinal cord obtained at various stages of development were determined for several lectins with specificities for a wide range of oligosaccharides. A discrete developmental change in the molecular-weight pattern was seen only among polypeptides binding the two Phaseolus vulgaris agglutinins, E-phytohemagglutinin (E-PHA) and L-PHA. With increasing maturity, the apparent molecular weights of the major polypeptides binding these two lectins progressively decreased. Furthermore, at all stages of development, E-PHA and L-PHA bound to the same polypeptides as the monoclonal antibody HNK-1, which recognizes a carbohydrate epitope on polypeptides that may play roles in cell adhesion. Based on the carbohydrate specificities of the two PHAs, we conclude that it is likely that the HNK-1 epitope resides on a triantennary N-linked oligosaccharide bisected by N-acetylglucosamine.