In order to meet the demand for safe transfusion in special conditions and to utilize the donated blood supply efficiently, technology has been developed to convert erythrocytes from type A, B, or AB to "universal donor" blood. Conversion of blood type B to O was performed by means of recombinant alpha-galactosidase digestion. The results showed that blood type B to O was converted successfully, 1 transfusion unit of red cells of group B (100 ml totally) could converted to universal blood cells in the optimal conditions including pH 5.6, 26 degrees C, 2 hours, obturation and sterilization. It is concluded that the universal red blood cells converted from group B to group O are conformed to demand of identification rules of biological products, no harmful effects of alpha-galactosidase on cell structure and function are observed. The converted red cells can stored in 4 degrees C for 21 days.