Human alpha-fetoproteins were purified from umbilical cord serum and from ascites fluid of a patient with hepatoma by affinity chromatography, and their chemical compositions and terminal sequences were compared. The amino acid compositions of these alpha-fetoproteins were similar and in good agreement with the values reported by other investigators. The COOH-terminal 5-amino acid sequence determined by carboxypeptidase digestion and the NH2-terminal 20-amino acid sequence determined by an automated sequence analyzer revealed that both alpha-fetoproteins had the same terminal sequences of amino acids. The sequence analysis showed that a part of each of the proteins lacked its NH2-terminal residues for one or three amino acids. A small difference in the carbohydrate composition of each alpha-fetoprotein was observed. It was concluded that alpha-fetoproteins from fetal serum and from ascites fluid of a patient with hepatoma had very similar structures.