Vitamin B_<12> in serum is bound to specific proteins, transcobalamins (Tc). By different separation techniques it is possible to separate one localized to the α-globulin fraction (Tc I) and the other to the β-globulin fraction (Tc II). The former is related to a larger extent to granulocytes. This report describes one patient with metastatic liver cancer, exhibiting an extraordinary elevation of Tc I in serum and ascites. Identification of Tc I was made by acid treatment, Quso G32 adsorption, Sepahdex G200 gel filtration and DEAE cellulose column chromatography. Although the patient had slightly increased white-cell counts, it was thought that the Tc I elevation was not due to leukocytosis but related to the the existence of metastatic liver cancer. It was likely but not proven that carcinoma cells produced Tc I like substance.