Red blood cell survival studies were performed on five normal growing swine by following the C14-specific activity of hemoglobin and heme after the administration of glycine-2-C14. The erythrocytes of normal growing swine appear to be destroyed both by a random and an age-dependent process. Random destruction accounts for the larger portion of the cells which are destroyed. The "mean" red cell survival time was 62 days. This represents the interval from the time of incorporation of 50 per cent of the maximal amount of labelling achieved to the time when the level had decreased once more to the 50 per cent amount. The " ‘corrected’ average potential life span" of the red cells was 86 ± 11.5 days. This figure was obtained by subtracting the number of days required to attain 80 per cent of the maximal labelling from the average survival time of red cells destroyed by an age-dependent process as distinguished from random destruction.