The hemoglobin of the european mole (Talpa europaea) has only one component. The alpha- and beta-chains were separated by chromatography on CM 52 cellulose. The primary structures of both chains were mainly established on the tryptic peptides by automatic Edman degradation. The N-terminal regions were sequenced on the chains. Large C-terminal peptides could be isolated and sequenced after acidic hydrolysis of the Asp-Pro bond (alpha: 94/95, beta: 99/100). The peptides were aligned by their homology with human alpha- and beta-chains. A comparison with human hemoglobin shows an exchange of 18 amino acid residues in the alpha-chains and of 30 in the beta-chains. The substitutions in the surroundings of the heme and the contacts between the subunits are discussed. All amino acid residues responsible for the binding of 2,3-dihosphoglycerate are present. Nevertheless a high oxygen affinity and a reduced interaction with diphosphoglycerate are found in mole hemoglobin (Jelkmann, W., Oberthür, W., Kleinschmidt, T. & Braunitzer, G. (1981) Respir. Physiol., in press). According to the sequence a relaxed structure of the central cavity between the beta-chains can be the reason for the low interaction between phosphate and protein. The oxygen affinity is not only affected by the presence of diphosphoglycerate-binding sites in hemoglobin but also by the structure in this region of the molecule.