Of 37 patients with histologically verified hepatocellular carcinoma (HCC) from Bangkok, Thailand, 34 had raised values of plasma cobalamin, and 1 presented with a markedly increased value of plasma transcobalamin I (TC I). One patient with clinical malignancy of the liver, not proven histologically to be HCC, had a raised plasma cobalamin value and a markedly increased value of TC I. From our own studies and from studies in the literature we find circumstantial evidence that TC I occasionally is produced by the malignant liver cells in HCC.