An immunological method for human hemoglobin assay was established, using which contents of fetal hemoglobin in the blood of hepatocellular carcinoma patients as well as in the extract of hehatocellular carcinoma tissue were measured. With the hemolysate, 4 out of 7 hepatocellular carcinoma cases showed slight but definite increase, 2 out of 10 in the serum and 6 out of 8 in the tissue extract. No such excess of fetal hemoglobin was found in cirrhosis or metastatic hepatic cancer cases as far as examined. Immunofluorescent study revealed that the mode of fetal hemoglobin distribution in the red blood cell in cases of hepatocellular carcinoma was quite similar to that in other instances of fetal hemoglobin increase, such as leukemia, aplastic anemia, etc. Immunochemical analysis of fetal hemoglobin appearing in cases of hepatocellular carcinoma again revealed quite the same character as the one existing in the normal cord blood. Discussions are made on the rationality in considering fetal hemoglobin as one of carcinoembryonic proteins on the one hand, on the similarity and difference between fetal hemoglobin and alpha-fetoprotein on the other.