Analysis of computer-generated data from 42,902 transfusions of red cells or whole blood reveals that 30 percent of Rh-positive and 46.5 percent of Rh-negative units of blood will be lost from inventory if the permissible storage time for blood is immediately reduced to 25 days. These data indicate that, should such a reduction be adopted as a means of preventing transfusion-transmitted Yersinia infection, the blood banking industry will have serious difficulties in maintaining an adequate blood supply.