ABO blood group polymorphisms of humans and other primates are determined by the expression of A, B, or H antigens, which are terminal neutral glycan sequences that are abundant in glycoproteins and glycolipids. H substance is a precursor which, under the influence of genes A and B, is converted into blood group substance A or B, respectively. Given that the inactive O allele does not alter H substance, the presence of unchanged H determinants is characteristic of blood group O individuals. ABH blood group antigens in human erythrocyte membranes occur as glycolipids and glycoproteins. Among blood group ABH glycolipids on erythrocytes, substances with type 2 chains are predominant. Glycolipids with type 3 and 4 chains are present only in insignificant amounts and type 1 chain glycolipids are adsorbed from the plasma because they are not endogenous erythrocyte substances. Blood group H active antigens have been found on O-linked and N-linked carbohydrate chains1–3. The H-specific oligosaccharide unit has been identified as the trisaccharide Fucα1-2Galβ1-3GalNAc-. In the majority of these H chains, N-acetylgalactosamine carries an α2-6 neuraminic acid residue, but this structure does not seem to have any serological activity4. The blood group H determinant in human erythrocytes is carried mainly by a lacto-series type 2 chain5. Type 3 chain glycolipids have been found only in group A erythrocytes. Type 3 substance is characteristic of group A1 erythrocytes and is present in only trace amounts in A2 cells. Precursor H type 3 occurs in greater quantities in A2 erythrocytes than in A1 erythrocytes, but is absent in O and B cells. As early as the mid-20th century, studies showed that some micro-organisms have enzymatic activities that can modify ABO type6. However, it was not until the 1980s that the pioneering work of Goldstein and Lenny (New York Blood Center, NY, USA) discovered technology for enzymatic conversion of A and B antigens which could be used in blood transfusion7. The general name used for the technological concept is “Enzyme-Converted group O Red Blood Cells” (ECO-RBC). Based on the ECO-RBC concept, glycosidase and glycosyltransferase were used to modify the structure of blood group H antigens. α-1,2-L-fucosidase is a highly specific exoglycosidase that catalyses the hydrolysis of α1-2 linked L-fucopyranosyl residues from oligosaccharides, whereas plasma-derived N-acetylgalactosaminyltransferases (A-transferase) transfer N-acetylgalactosamine residues onto galactose residues in H determinants in the presence of UDP-N-acetylgalactosamine. In this study, we used α-1,2-L-fucosidase to modify the structure of type 2 chain H. The modified antigens did not show type 2 chain H antigen activity. The erythrocytes treated by fucosidase are called FM-erythrocytes. We used the A-transferase from A1 plasma to modify the structure of type 3 chain H antigens. The erythrocytes treated by A-transferase are called TM-erythrocytes.