Directed cell migration involves signaling events that lead to local accumulation of PI(3,4,5)P 3 , but additional pathways act in parallel. A genetic screen in Dictyostelium discoideum to identify redundant pathways revealed a gene with homology to patatin-like phospholipase A 2 . Loss of this gene did not alter PI(3,4,5)P 3 regulation, but chemotaxis became sensitive to reductions in PI3K activity. Likewise, cells deficient in PI3K activity were more sensitive to inhibition of PLA 2 activity. Deletion of the PLA 2 homolog and two PI3Ks caused a strong defect in chemotaxis and a reduction in receptor-mediated actin polymerization. In wild-type cells, chemoattractants stimulated a rapid burst in an arachidonic acid derivative. This response was absent in cells lacking the PLA 2 homolog, and exogenous arachidonic acid reduced their dependence on PI3K signaling. We propose that PLA 2 and PI3K signaling act in concert to mediate chemotaxis, and metabolites of PLA 2 may be important mediators of the response.