THE eosinopenia induced by epinephrine is well known, although the entire mechanism responsible for this effect is still not well understood. Factors other than a responsive adrenal cortex seem capable of evoking an eosinopenic response to epinephrine. The discovery of nor-epinephrine has been followed by several investigations of the ability of this compound to induce eosinopenia. Thorn et al. (1) have stated that nor-epinephrine is practically devoid of eosinolytic effect. The results of several investigations of the comparative eosinolytic effects of epinephrine and norepinephrine in normal fasting human subjects and in the mouse indicate that the latter is approximately one-sixth as potent as the former in this respect (2–5). This study was undertaken to confirm and extend previous investigations of the relative eosinolytic properties of epinephrine and nor-epinephrine, with special reference to their effect upon patients with disorders not involving endocrine organs and in patients with impaired adrenocortical and anterior pituitary function.