Leukocyte depletion may limit the inadvertent infusion of bioactive substances derived from polymorphonuclear leukocytes, of which HNE is but one example. The accumulation of HNE in buffy-coat-reduced red cells may be greater than that of whole blood units. HNE accumulates during storage and its quantity may have pathophysiologic significance. Platelets and plasma derived from buffy coats contain some HNE, but leukocyte-depleted red cells virtually none. However, we consider the accumulation of HNE in these components not to be clinically important. The quantities, kinetics, and occurrence in various blood components of HNE contamination differ from those observed with cytokines.