One-half million cases of septicemia are reported annually with a mortality of around 35%. Diagnosis depends in part on blood cultures which require one to two weeks. It would be advantageous if an early sign of septicemia were available. Cytoplasmic vacuolation of polymorphonuclear neutropnils is occasionally seen in the peripheral blood smears of patients who have infections. The object of this work was to determine the cause and significance of cytoplasmic vacuolation with the goal of using the occurrence of vacuolation as an early indicator of infection.