Abstract: A method of freezing a standard donor unit of red blood cells such that it can be stored for long periods and subsequently recovered in a form pure enough for transfusion purposes involves centrifuging a blood unit to remove plasma and platelets and to provide a Packed Cell Volume of the red blood cells of not less than 90%, adding the red blood cells to a freezing bag, containing HES solution such that the ratio of HES/red blood cell freezing unit is not more than 7% (preferably 6%) w/v, positioning the freezing bag in a freezing frame adapted to maintain the thickness of the contents of the bag constant, and placing the frame without shaking, into liquid nitrogen.