The complete amino acid sequence of the major component myoglobin from Pacific common dolphin, Delphinus delphis, was determined by the automatic Edman degradation of several large peptides obtained by specific cleavages of the protein. More than 80% of the covalent structure was established by the degradation of the apomyoglobin and five peptides from: (1) cyanogen bromide cleavage at the two methionine residues, (2) trypsin cleavage of the acetimidated apomyoglobin at the three arginine residues, and (3) 2-p-nitrophenylsulfenyl-3-methyl-3'-bromoindolenine cleavage at the two tryptophan residues. The rest of the sequence was determined by use of the peptides prepared from further digestion of the central cyanogen bromide peptide with staphylococcal protease and trypsin. The primary structure of this myoglobin proved identical with that from the Atlantic bottlenosed dolphin, Tursiops truncatus, but showed four substitutions with respect to the sequence reported for the Black Sea dolphin which has also been given the designation Delphinus delphis.