Phosphate compounds of red cells stored at 4 degrees C. in acid-citrate-dextrose solution for 15 to 44 days, incubated at 37 degrees C. for 2 and 4 hours with inosine, pyruvate, and inorganic phosphate, and then stored for 2 weeks have been examined by ion-exchange column chromatography. After 2 and 4 hours of incubation the 2,3-diphospholycerate level increased to 1,385 and 1,819 mumoles per 100 ml. of erythroeytes, respectively. After 4 hours of incubation the content of AIP increased to about 80 per cent of the physiologic level, while the content of AMP and ADP decreased considerably. These data suggest that the elevation of ATP is in part connected with the phosphorylation of AMP and ADP. The incorporation of inosine or hypoxanthine into the IMP and ITP has been proved. Four hours incubation period caused the synthesis of IMP and ITP to the mean value of 187 and 141 mumoles per 100 ml. of erythrocytes, respectively. No evidence of IDP formation was observed during the chromatographic separations of erythrocytic phosphate compounds. Storage of the erythrocyte suspension which has been incubated for 4 hours leads to the slower decomposition of 2,3-diphosphoglycerate, ATP, ITP, and IMP, and to the increase of AMP and ADP.