The hemoglobin of the egyptian fruit bat (Rousettus aegyptiacus) has only one component. The alpha and beta chains were separated by chromatography on CM-52 cellulose. The complete primary structures of both chains were established by automatic Edman degradation of the chains and the tryptic peptides. The alignment was done by homology with alpha and beta chains of adult human hemoglobin. A comparison of these two hemoglobins shows an exchange of 14 amino acid residues in the alpha chains and of 19 in the beta chains. These numbers are very low, considering the long phylogenetic distance between primates and megachiroptera. In the surroundings of the heme we found one substitution in each chain. In the alpha 1 beta 1-subunit interface one and two residues are exchanged respectively in the alpha and beta chains. The primary structure points to a normal oxygen affinity of the bat hemoglobin which was also found by Jürgens et al.