Ninety-eight units of AS-1 red cells (RBC) were studied to determine the optimal unit age for the preparation of leukocyte-poor red cells by the spin-cool-filter method. After 1 week of storage, the residual leukocyte counts of AS-1 units prepared by this method averaged 0.5 .times. 109 or fewer white cells, which indicated removal of more than 79 percent of the total white cells. The spin-cool-filter method. In conjunction with the rapid degeneration of the white cells in the AS-1 RBC, yielded leukocyte-poor units comparable to those prepared from citrate-phosphate-dextrose-adenine (CPDA-1) RBC.