Tryptic peptides of the α and β chains from silvery marmoset (Callithrix argentatus) and cotton-headed tamarin (Saguinus oedipus) hemoglobins were isolated and sequenced, respectively, by conventional methods. The ordering of the peptides in each chain was deduced from the homology of their sequences with those of human adult hemoglobin. The primary structures thus deduced are compared with those of other primate hemoglobins, and the rate of evolution in New World monkey hemoglobins is discussed.