Endogenous lactose-binding proteins from adult chicken liver and intestine have been purified to homogeneity by affinity chromatography on asialofetuinderivatized Sepharose, followed by isoelectric focusing. Since these carbohydrate-binding proteins are assayed as hemagglutinins, they are referred to by the operational term lectins. Although the hemagglutination activity of these lectins is inhibited by similar concentrations of inhibitory saccharides, they are not the same. They differ in specific hemagglutination activity, subunit molecular weight, and isoelectric point. They have very different peptide maps and show no detectable immunological cross-reactivity. Based on gel filtration studies, the liver lectin behaves as a dimer with apparent Mr = 31,000 +/- 1100, whereas the intestinal lectin behaves as a monomer with apparent Mr = 14,000 +/- 1700. Although clearly different from the intestinal lectin, the lectin from adult liver appears identical with the lectin previously purified from embryonic skeletal muscle.