Factors present in supernatants prepared from neural retina or cerebral lobe tissue cultures bind specifically to cells of the same type and promote cellular aggregation; the basis for the specificity of these factor-cell interactions has been investigated. Pronase digestion destroys binding of protein but not the carbohydrate portion of factors. Digestion with a mixture of protease-free glycosidases destroys both protein and carbohydrate binding. Purified beta-N-acetylhexosaminidase reduces binding of retina factor by 80%. The enzymatic activity which destroys binding of cerebral lobe factor to cerebral cells appears to be alpha-mannosidase activity. Further, paper chromatography of the enzymatic digestion products of the binding factors reveals that N-acetylgalactosamine residues are released from the retina factor while mannosamine residues are released from the cerebral lobe factor. Inhibition of binding of factors to cells by monosaccharides is consistent with the enzyme data. N-Acetylgalactosamine maximally inhibits binding of factor to retina cells while mannosamine inhibits factor binding to cerebral cells. These data suggest that the specificity of cellular adhesion is determined, at least in part, by the sequence of sugars in an oligosaccharide residue of a complex glycoprotein.