Polyglycosyl peptides were isolated from delipidated erythrocyte membranes of human blood-group A1 and A2 erythrocytes by extensive pronase digestion and gel filtration. As estimated by the amounts of N-acetylgalactosamine and 2-O-substituted galactose residues about 85% of the possible acceptor sites (H determinants) were saturated with A determinants in A1 polyglycosyl peptides whereas only 25% of H sites were filled in A2 glycopeptides. The distribution of A and H determinants in the glycopeptides was studied by affinity chromatography with Sepharose-bound Bandeiraea simplicifolia I-lectin (binds blood-group A and B determinants) and Ulex Europeaus I-lectin (binds blood-group H determinants). About 55% of the polyglycosyl peptides contained A, H, or A and H determinants in both A1 and A2 blood subgroups. 48% of the polyglycosyl peptides of blood group A1 and 10% of A2 bound to Bs I-lectin. 25% of the polyglycosyl peptides in A1 and 53% in A2 carried H determinants. The molecular size, monosaccharide composition and the substitution pattern of the monosaccharides in the Bs-I-bound polyglycosyl peptides were very similar in both A1 and A2 blood groups. The only difference was the amount of N-acetylgalactosamine which was on the average 3.7 mol/mol in A1 and 2.5 mol/mol in A2. The active fraction was found to be heterogeneous with respect to the amount of A determinants, which varied from 1 to 6 per glycopeptide in A1 and A2 polyglycosyl peptides. The findings do not indicate a structural difference between blood-group A1 and A2 polyglycosyl peptides and state chemically that A1 glycopeptides contain more A determinants than A2 glycopeptides.