A full-length clone encoding the mouse erythrocyte anion exchange protein, band 3, has been isolated from a cDNA library using an antibody against the mature erythrocyte protein. The complete nucleotide sequence has been determined. Substantial homology is evident between the deduced murine amino acid sequence and published sequences of fragments of human band 3 protein. The amino-terminal 420 and the carboxy-terminal 32 residues constitute polar, soluble domains, while the intervening 475 amino acids are likely to be intimately associated with the lipid bilayer. Hydrophobic analysis of this sequence, together with structural studies on the human protein, suggests the possibility of at least 12 membrane spans, predicting that both the amino- and carboxy-termini are intracellular.