Using polymerase chain reaction, bottle-nosed dolphin (Tursiops truncatus) major histocompatibility complex (DoLA) class I alpha chain cDNA was cloned and sequenced. Predicted amino acid sequences of DoLA class I alpha chain have cystein residues for intradomain disulfide bond formation and N-linked glycosylation sites, suggesting that DoLA class I alpha chain molecules construct alpha 1, alpha 2, and alpha 3 domain structures. Similarity of DoLA class I alpha chain cDNA to land mammal MHC class I alpha chain cDNA was 90.4% in cattle, 90.2% in horse, 89.4% in sheep, and 87.8% in human. This investigation suggests that DoLA is closely related to land mammals.