The primary structure of adult marmoset hemoglobin has been determined. The alpha- and beta-chains of HbA were separated on a CM23 column in 8 M urea using a sodium phosphate gradient. Tryptic digest of the alpha- and beta-chains were fractionated on a Dowex 50W-X2 column using a pH and pyridine acetate gradient. Large peptide fragments were obtained by the cyanogen bromide cleavage of the alpha- and beta-chains, as well as by tryptic digestion of the maleylated alpha- and beta-chains. The sequence was derived from the amino acid compositions and sequences of the individual tryptic peptide, automated sequence determination of intact alpha- and beta-chains, as well as automated sequence determination of cyanogen bromide fragments and tryptic maleylated peptides derived from the alpha- and beta-chains. The complete structure of marmoset adult hemoglobin is closely homologous to that of other primate hemoglobins. The sequence of the marmoset alpha-chain differs from the alpha-chian of human HbA at positions 8, 19, 23, 68, and 116. The beta-chain from marmoset HbA differs from the beta-chain of human HbA at positions 5, 13, 21, 50, 87, and 125.