Bilateral adrenalectomy reduced the effect of half-body X-ray exposures, ranging from 50 to 800 r, on the peripheral leukocyte count of rats. Neutrophils and lymphocytes were spared in similar measure by adrenalectomy and the total leukocyte count returned to normal sooner in adrenalectomized rats than in controls. These effects were conspicuous in the 250 to 400 r range. It is assumed that withdrawal of adrenal function exerts a protective action on lymphoid as well as myeloid tissues which maintain a ready supply of lymphocytes and neutrophils to the peripheral blood.