The sequential changes of formed blood elements and chemical components that occur in acid-citrate-dextrose blood in plastic bag during storage at 4℃ for 21 days have been observed. With the storage time, hemoglobin, hematocrit, and red blood cell, white blood cell and platelet courts were decreased, especially in platelet count. The level of potassium, ammonia, LDH, plasma hemoglobin and acid phosphatase were marked1y increased whereas dextrose, sodium and chloride were decreased. BUN, uric acid, GOT, protein and albumin were not changed.