1. Thirty-seven normal subjects were given subcutaneous injections of epinephrine, ranging from 0.25 to 0.5 mg., and the effects on the leukocytes were noted.
2. The neutrophils rose steadily for the three and one-half hours during which blood counts were made. The small lymphocytes rose in the first half hour, then fell below normal and finally returned towards normal. The eosinophils rose at first and then fell below normal for the remainder of the period.
3. The three doses of epinephrine used produced effects which differed quantitatively but not qualitatively. The most readily identified effect of the smallest dose was the one-half hour rise in lymphocytes or the one-half hour rise in total count. A dose of 0.5 mg. is satisfactory for work of this kind.
4. Subjects with a history of allergy showed a greater tendency than the remainder to exhibit a one-half hour rise in the eosinophil count.
5. The changes in the leukocyte count produced by epinephrine are similar to, but not identical with, those produced by adrenocortical hormone or adrenocorticotropic hormone.
ACKNOWLEDGMENTS We are indebted to the Faculty Research Committee of the University of Pennsylvania for a grant to one of us (C. W.) towards the expenses of this investigation.