High capacity adsorbents for lectins, including Lotus tetragonolobus L-fucose-binding protein, were readily prepared by conjugation of monosaccharides with commercially available, epoxy-activated Sepharose. Purified, radioiodinated lectins were bound to cells of the mosquito Aedes aegyptii and of human KB tumour. Relative to human KB cells, mosquito cells bound less of lectins specific for the sugars (L-fucose and D-galactose) that are terminal residues in many mammalian glycoproteins, whereas the number of binding sites of lectins specific for core-region sugars (D-mannose and 2-acetamido-2-deoxy-D-glucose) were similar. Neuraminidase, which greatly enhanced binding of peanut agglutinin or soybean agglutinin to human KB cells, had negligible effects on binding of these lectins to mosquito cells. The comparative structures of surface oligosaccharides of mosquito and KB cells are discussed in relation to the lectin-binding studies.