Time course digestion of intact human erythrocytes and right side-out vesicles with carboxypeptidase Y altered the Rh polypeptides and removed the 125I label that is normally incorporated by cell-surface radioiodination, but did not affect the RhD, Rhc, or RhE antigens. Under the same conditions, however, the LW antigens were rapidly destroyed. Digestion of inside-out and right side-out vesicles with aminopeptidase M was without any detectable effect on the Rh and LW antigens or polypeptides, although glycophorin A was degraded from right side-out but not from inside-out vesicles. These findings demonstrate that the C-terminal domain of the Rh and LW polypeptides is exposed at the external surface of human erythrocytes and indicate, in addition, that the LW antigens and tyrosine residue(s) of the LW and Rh proteins, respectively, are located close to the C termini of these polypeptides. Further studies using monoclonal and polyclonal antibodies showed that LW antigen expression is inhibited by treatment of red cells with EDTA and is selectively restored by Mg2+, but not by Mn2+ or Ca2+, whereas the Rh antigens were not affected under these conditions. In addition, O- and N-glycanase digestion of the LW glycoprotein removed its sugar chains, but did not alter significantly the epitopes recognized by the monoclonal anti-LW antibody.