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The freezing of blood permits preservation of red cells over long periods of time, several months or years. Leucocyte and platelet contamination of red cell concentrates to be frozen is negligible. The amount of the various red cell metabolites (2.3 D.P.G., A.T.P., etc.) is maintained. Washing of thawed red cells removes the remaining plasma proteins and cell residues. The freezing method employed is that of Row et al. The protector used is 28% glycerol added in equal amounts to red cell concentrate to be frozen. The blood bag is kept in liquid nitrogen at -- 196 degrees C. Thawing takes place in a water bath at 45 degrees C. Wash solution is the IBM Blood regenerator. The solution used for removing glycerol is hypertonic natrium chloride. The following parameters have been investigated: --hemoglobin level; --osmotic fragility; --the amount of 2.3 D.P.G.; --residual glycerol after thawing; and clearance of leucocytes and platelets following each step of the protocol. Preliminary data regarding these features and therapeutic efficiency of processed blood are satisfactory.