Excretion of parenterally administered Fe is approx. 5 to 10 times as great in feces as in urine. The rate of excretion varies with the location of the tracer within the various Fe pools in the body (e.g., cells, liver, reticulo-endothelial system). This is illustrated by high plasma levels of Fe59, associated with high excretory rates in feces and urine. 55 days after injn.of Fe59 there is a 2d max. in excretory rate which can be shown to correspond with a loss of Fe59 from the largest pool, the circulating erythrocytes. When "Fe-3 Specific" (a commercial chelating agent manufactured by Bersworth Chemical Co., Framingham, Mass.; its structure was not revealed) is admd. intraperit. to animals which have been given Fe59, there is a prompt and marked increase in both the urinary and fecal excretory rates by a factor of 2 to 2.5. Addition of "Fe-3 Specific" to the diet of rats causes an increase in the fecal and urinary excretion of intraven. admd. ratio-Fe by approx. a factor of 2.3. When Fe59 and "Fe-3 Specific" are fed simultaneously, a marked increase in urinary excretion of the tracer occurs. However, the amt. found in feces is nearly the same as in controls. Thus the decrease in net retention resulted primarily because of increased urinary excretion. Feeding as much as 9.6 g.of "Fe-3 Specific" to animals at a rate of 400 mg./day was not associated with any change in hematocrit nor any grossly observable abnormality in the animals.