The amino acid sequences of tryptic, chymotryptic and cyanogen bromide cleavage peptides of the lac-tate dehydrogenase isozyme M4 from giant panda have been determined. Based on the overlapping peptidesand by a comparison with the known sequence of porcine lactate dehydrogenase isozyme M subunit, thecomplete primary structure of the giant panda lactate dehydrogenase isozyme M subunit has been estab-lished. The polypeptide chain of giant panda lactate dehydrogenase isozyme M subunit consists of 331amino acid residues. There is a variance of 17 amino acid residues between the porcine and the giantpanda lactate dehydrogenase isozyme M subunits. Most of the variable residues are substitutions bychemically similar amino acids and take place at residues not related to the active center of the enzyme. The amino acid sequences of tryptic, chymotryptic and cyanogen bromide cleavage peptides of the lac-tate dehydrogenase isozyme M4 from giant panda have been determined. Based on the overlapping peptides and by a comparison with the known sequence of porcine lactate dehydrogenase isozyme M subunit, the complete primary structure of the giant panda lactate dehydrogenase isozyme M subunit has been estab-lished. The polypeptide chain of giant panda lactate dehydrogenase isozyme M subunit consists of 331 amino acid residues. There is a variance of 17 amino acid residues between the porcine and the giant panda lactate dehydrogenase isozyme M subunits. Most of the variable residues are substitutions by chemically similar amino acids and take place at residues not related to the active center of the enzyme.