One-dimensional and two-dimensional peptide-mapping techniques are used to identify the protein which gives rise to the 72,000 dalton alpha-chymotryptic fragment previously shown to be the membrane attachment site for spectrin. Peptide maps of the 72,000 dalton fragment are very different from maps of Bands 1, 2, 2.9, 3, 3.1, 4.1, and 4.2 and very similar to maps of the apparently closely homologous polypeptides, Bands 2.1, 2.2, 2.3, and 2.6. Limited proteolysis of erythrocyte membranes is shown to generate Band 3', another polypeptide which has been associated with spectrin-binding activity. Peptide maps of Band 3' are very similar to maps of Band 2.1, suggesting that Band 3' is also a proteolytic fragment of Band 2.1. It is concluded that Band 2.1 and possibly some or all of the other, related polypeptides which electrophorese in the 2 region is (are) the spectrin-binding protein(s) of the human erythrocyte.