Abstract 1. 1. Seven distinct benzidine-positive bands were found on starch-gel electrophoresis at pH 8.6 of the hemolysates from fetal, newborn and adult golden hamsters. Four of the seven benzidine-positive bands were analyzed and named Hemoglobins I, II, III and IV according to their increasing electrophoretic mobility. Hemoglobins I and II were found as major components in the fetal stage. Hemoglobin I gradually decreased and disappeared by the 11th day after birth. Hemoglobin II, however, gradually decreased but remained as a minor component in the newborn and adult. Hemoglobins III and IV were found as minor components in the fetal stage, the former as a major component and the latter as a minor one in the newborn and adult stages. 2. 2. The amino acid compositions of the polypeptide chains from these hemoglobins were determined. Few differences among the αI, αIII and αIV chains were found in the amino acid compositions. There were apparent differences between the αII and other α chains involving a minimum of eleven amino acid residues. Among the non-α chains, the βII chain was very similar to the βIII chain and there were distinct differences among the γI, βIII and βIV chains. 3. 3. The tryptic peptide patterns of the aminoethylated (AE) αI, AE αII and AE αIV chains were closely similar to one another. In the patterns of the AE αIII and AE αII chains, one peak of the AE αIII was replaced by one acidic peak and two basic peaks of the AE αII chain. On the other hand the AE γI, AE βIII and AE βIV chains were quite different from one another in the tryptic pattern, while the pattern of the AE βII chain was similar to that of the AE βIII chain.