Autoradiographic Studies of Eosinophil Kinetics: Effects of Cortisol*

The effect of cortisol administration upon the labelling of blood eosinophils was studied in rats given a single injection of 3 H‐thymidine. One dose of cortisol did not change the subsequent course of labelling of eosinophils, whereas steroid treatment for 3 days resulted in a delay of the most heavily labelled class. The results seem to indicate that cortisol causes a reversible sequestration of blood eosinophils; and that long‐term steroid administration may delay the release of eosinophils from the bone marrow into the blood.