Three neuroblastoma systems were used to define fucose-containing glycopeptides on the cell surface and to relate them to the phenotypic expressions of neuronal functions. These systems were a) clonal lines of mouse neuroblastoma C-1300, b) cell hybrids of mouse neuroblastoma and rat glioma, and c) human neuroblastomas, primary cells from the tumor, and cell lines. The results suggest that similarities exist in the membrane glycopeptides available at the surface of the mouse and human cells. It is proposed that these similarities correspond to the ability of the cells to perform the differentiated functions of neuronal cells or to exist as tumors. Based on analogy with other cell membranes, a schema is given for the structure of the membrane glycopeptides on the neuroblastoma cell.