Glycoproteins (PNABGP : PNA binding glycoproteins)possessing inhibitory activity against hemagglutination of PNA, a lectin specific for Galβ(1→3)Gal NAc linkage in the non-reducing end of carbohydrate chains, were detected in the serum of patients with malignant tumors. These glycoproteins were purified from ascites collected from patients bearing carcinoma of the liver, pancreas and stomach by affinity chromatography using PNA, anti-whole human serum and anti-cirrhotic ascitic fluid. SDS-polyacrylamide gel electrophoresis of these glycoproteins yielded are main band (120K daltons). Using this preparation, PNABGP in the serum was quantitated by an enzyme-linked immunosorbent assay (ELISA). The levels of these glycoproteins were high in hepatocellular carcinoma and other malignancies.