The effect of ages of RBC donors on the elimination of ⁵¹Cr-labeled RBCs. RBCs were collected from CBA-+/+ (○) and -Pk-1^slc/Pk-1^slc (•) mice of various ages, labeled, and injected into 90-day-old CBA-+/+ mice. The radioactivity retained in RBCs was measured at various times after the transfusion and the percentage was plotted semi-logarithmically. Each point represents the mean of eight mice. In all points the standard error was too small to be shown by bars.