α and β chains from adult hemoglobin of the slender loris (Loris tardigradus) were isolated by Amberlite CG-50 column chromatography. After S-aminoethylation, both chains were digested with trypsin and the amino acid sequences of the tryptic peptides obtained were analyzed. Further, the order of these tryptic peptides in each chain was deduced from their homology with the primary structures of a and β chains of human adult hemoglobin. Comparing the primary structures of the α and β chains of adult hemoglobin of the slender loris thus obtained with those of adult hemoglobin of the slow loris, 4 amino acid substitutions in the α chains and 2 in the β chains were recognized.