• Affinity electrophoresis was used to study the sugar binding heterogeneity of lectins of their derivatives. • Commercial and demetallized preparations of concanavalin A could be resolved by affinity electrophoresis into three components with different affinity to immobilized sugar. Similarly the Vicia cracca lectin obtained by affinity chromatography behaved on affinity gels as a mixture of active and inactive molecular species. • Affinity electrophoresis has shown that the nonhemagglutinating acetylated lentil lectin and photo-oxidized or sulfenylated pea lectin retain their sugar binding properties; dissociation constants of saccharide complexes of these derivatives are similar to those of native lectins. • The presence of specific immobilized sugar in the affinity gel improved the resolution of isolectins from Dolichos biflorus and Ricinus communis seeds. resolution of isolectins from Dolichos biflorus and Ricinus communis seeds.