A fucose-binding lectin from fruiting bodies of Aleuria aurantia was purified by affinity chromatography by using the H-active glycopeptide of desialyzed porcine submaxillary mucine coupled to Sepharose 4B and eluting with L-fucose. Homogeneity of the active protein was confirmed by polyacrylamide gel electrophoresis, isoelectric focusing, column chromatography using Sephadex G-100, and ultracentrifugal analyses. It has a molecular weight of 72 000 and is proposed to be a dimer of identical subunits, each of which has combining site of uniform affinity. Chemical analyses revealed the absence of the sulfur-containing amino acid and carbohydrate, neutral and amino sugar, in the lectin molecule. It agglutinated human erythrocytes of all ABO and Lewis types, Bombay phenotype, and group O cells treated with alpha (1 leads to 2)-fucosidase. In double-diffusion experiments, the lectin formed a single precipitin line which fused with all of the fucose-containing blood-group substances tested, including the alpha-fucosidase-treated materials. These findings together with the results of hemagglutination and precipitation studies indicate that the lectin combines the terminal fucose in the carbohydrate chain but doses not require a particular linkage to the penultimate sugar moiety.