The autoradiographic detection of ¹²⁵I-labeled lectins binding to glycolipids on thinlayer chromatograms can be used to rapidly analyze total glycolipid extracts of cells or tissues for specific oligosaccharide structures. The Helix pomatia lectin which binds with high affinity to terminal α-linked GalNAc residues did not bind to globoside (terminal β1-3GalNAc) but did bind the ganglioside GM₂ and its asialo derivative which have terminal β1-4GalNAc residues. The lectin from Dolichos biflorus bound specifically to the Forssman glycolipid with relatively low affinity. The lectin from Wisteria floribunda was bound to Forssman glycolipid, globoside, and the asialo derivative of the ganglioside GM₂. The interactions of these lectins with the glycolipid-derived, ³-labeled oligosaccharides was also analyzed by affinity chromatography. The results indicated that the reactivity of multivalent carbohydrate-binding proteins with polyvalent surfaces of glycolipids is strong enough to permit detection of low-affinity interactions that may not be observed in binding assays that are based on carbohydrate-protein interactions in solution. The autoradiographic analysis of ¹²⁵I-Helix pomatia lectin binding to thin-layer chromatograms of total lipid extracts from human erythrocyte membranes detected the quantitative differences in the A-active glycolipids from type A₁ and A₂ Cells.