We surveyed the calcium-requiring (C-type) lectins in alligator liver. The major lectin purified by affinity chromatography was termed alligator hepatic lectin (AHL) and was found to be specific for mannose/L-fucose. AHL contained approximately equal amounts of 21- and 23-kDa bands upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Binding characteristics of AHL were similar to those of hepatic lectins of other classes in that 1) only terminal monosaccharide was recognized, and 2) the affinity increased exponentially when neoglycoproteins containing increasing numbers of mannose or L-fucose were used as ligand. However, unlike mammalian and chicken hepatic lectins, which exist as hexamers in Triton-containing solutions, AHL was present mainly as monomers, although small amounts of dimer and higher oligomers were present in equilibrium. Mannose-binding proteins and mannose-specific lectins of macrophages bind N-acetylmannosamine, glucose, and N-acetylglucosamine in addition to mannose, indicating that the nature and orientation of the C-2 substituent are not important to these lectins. In contrast, AHL shows a strict requirement for the presence of an axial hydroxyl group at the C-2 position (i.e. mannose).