The primary structures of the .beta.-chains from pig (Suidae) and llama (Lama glama, Camelidae) Hb are given. They differ from human .beta.-chains in the exchange of 22 and 23 amino acid residues, respectively. Some aspects of the sequences are discussed and the molecular interpretation of respiration at high altitudes is given. This interpretation is based on the exchange of the 2,3-diphosphoglycerate contact .beta.2His.fwdarw.Asn from man to llama: the interaction between the heterotropic allosteric effector 2,3-diphosphoglycerate and protein is diminisihed, which results in higher O2 affinity of the Hb of llama. The placental respiration and the high-altitudes respiration have the same molecular mechanism.