A lectin from Thai marine carb (Scylla serrata) hemolymph has been isolated and purified by affinity column chromatography and preparative electrophoresis. The amino acid composition and 10 amino-terminal residues have been deduced, and its reactivities have been studied using a biotin labeling technique. A method for the determination of sialoglycoconjugates in human serum is described using this lectin. The principle is based on the reaction between the sialoglycoconjugates and biotinylated lectin. The bovine submaxillary mucin (BSM) is immobilized on polystyrene microplate. The unknown sample or sialoglycoconjugate (BSM equivalent) standards, together with excess biotinylated purified lectin (B-lectin), are then added. The B-lectin that binds to the immobilized BSM is then incubated with the peroxidase-conjugated monoclonal antibiotin antibody, and the color that develops after the addition of enzyme substrate is determined by light absorption using a microplate reader. The assay is not only convenient and reliable, but also capable of measuring sialoglycoconjugates in solution at the submicrogram level. It was used in determining the sialoglycoconjugates in human serum from normal subjects and samples positive for carcinoembryonic antigen.