Cell surface molecules have been implicated in cell interactions which underlie formation of the nervous system. The analysis of the functional properties of such molecules has profited from the combined use of antibodies and cell culture systems. It has been suggested that the interplay between these molecules modulates cell-to-cell interaction at critical developmental stages. In the mouse, N-CAM and L1 antigen have been shown to mediate Ca2+-independent adhesion among neural cells. N-CAM plays a role in fasciculation of neurites and formation of neuromuscular junction. L1 is apparently not involved in synaptogenesis, but in migration of granule cell neurones in the developing mouse cerebellar cortex. The two antigens are distinct molecular and functional entities which act synergistically in aggregation of neuroblastoma and early postnatal cerebellar cells. In view of a certain similarity in function between the two groups of molecules, it was not surprising to find that structural similarities are detectable by the monoclonal antibody L2. We show here that a carbohydrate moiety recognized by L2 and HNK-1 monoclonal antibodies, is present in mouse N-CAM and L1. The L2 epitope appears on all major neural cell types but not all N-CAM molecules express it. This heterogeneity points to a previously undetected molecular diversity which may have functional implications for modulating cell adhesion during development.