This research dealing with fish, bird and mammal hemoglobins is in the framework of the study of the molecular basis of cold adaptation in Antarctic organisms. The study of hemoglobin structural and functional properties in Antarctic teleosts allowed a correlation of amino acid sequence, multiplicity, and oxygen‐binding features with ecological constraints. Amino acid sequences of α and β chains were analysed to build phylogenetic trees, while the organisation and expression of globin genes was studied. The respiratory proteins of Antarctic birds were investigated, in relation with the oxygen demands arising from their characteristic behaviour (diving or flight) and, in general, from the extreme conditions of the Antarctic habitat. The study of Weddell seal hemoglobins indicated that the combined effect of carbon dioxide, organic phosphates and temperature optimises oxygen delivery to all tissues in spite of their relative heterothermia. The crystallographic structure of the carbonmonoxy derivative ofTrematomus newnesimajor hemoglobin was resolved, giving new insight into the study of the Root effect. The molecular models of skua hemoglobins revealed the presence of a second, additional phosphate binding site located between the two α chains, paving the way to further studies.