The erythrocyte receptors for Vicia graminea (Vg) anti-N lectin have been investigated after 125I-labelling of the purified lectin and binding to membrane components separated by dodecyl sulphate polyacrylamide gel electrophoresis. GP alpha (synonym glycophorin A or MN glycoprotein) and GP delta (synonym glycophorin B or Ss glycoprotein) are the main Vg receptors of native human blood group NN and MN erythrocytes whereas Vg lectin only binds to GP delta from MM red cells. The glycoprotein of 28 kDa present in Mi III erythrocytes (a presumed variant of GP delta) carries Vg receptors. Both binding studies and agglutination experiments with this lectin suggest that the delta Mi III gene might produce more glycoprotein molecules than the normal delta gene. Binding of Vg lectin to hybrid glycoproteins [from Mi V, St(a+) and Dantu (+) donors] produced by unequal crossing-over between alpha and delta genes, may occur if the molecules exhibit N activity. The lectin does not bind to sialic acid- and galactose-deficient glycoproteins from Tn erythrocytes and no binding could be detected in the region of GP delta of erythrocytes from S-s-U-individuals. Addition of N-acetylgalactosamine residues to the alkali-labile oligosaccharides attached to GP alpha and GP delta, as found in Cad erythrocytes, decrease the binding capacity for Vg lectin. Finally the absence of Vg lectin binding sites on native GP alpha molecule from MgMg and McM erythrocytes, which carry well defined variants of this glycoprotein, supports the view that the binding site of the lectin on native glycoproteins is located at the N-terminal end of glycoprotein (GP alpha and GP delta) with N specificity (N-terminus = Leu).