It is often baffling to the surgeon when after an operation a patient takes an unexplained turn for the worse or follows a progressively downhill course without apparent reason. I have recently observed that in association with such a course examination of the blood frequently shows leukopenia, with a normal differential count and a marked shift to the left of the neutrophils. This picture signifies a wearing out of the leukopoietic power and offers an explanation of the patient's lack of response to ordinary measures. This leukocyte exhaustion always indicates a serious prognosis and is probably more common than is generally realized. It therefore, I believe, deserves more recognition as a complication following surgical procedures. Leukocyte exhaustion was first described by Turk1 in 1907 and is usually considered as due to the "overwhelming irritation" of severe sepsis (Schilling2) or to "long continued infection as the result of a