Polymorphonuclear leukocyte chemotaxis has been elicited by oxidized arachidonic acid and other oxidized polyenoic lipids in the Boyden micropore filter assay system. This chemotactic activity was observed in the absence of serum and chemotactic proteins. The esterfied arachidonic acid present in plasma membranes may be a precursor of chemotactic messages as well as prostaglandins in vivo.