Experimental autoimmune encephalomyelitis (EAE), a Th1-mediated inflammatory disease of the central nervous system (CNS), is a model of human multiple sclerosis. Cytosolic phospholipase A₂α (cPLA₂α), which initiates production of prostaglandins, leukotrienes, and platelet-activating factor, is present in EAE lesions. Using myelin oligodendrocyte glycoprotein (MOG) immunization, as well as an adoptive transfer model, we showed that cPLA₂α^−/− mice are resistant to EAE. Histologic examination of the CNS from MOG-immunized mice revealed extensive inflammatory lesions in the cPLA₂α^+/− mice, whereas the lesions in cPLA₂α^−/− mice were reduced greatly or completely absent. MOG-specific T cells generated from WT mice induced less severe EAE in cPLA₂α^−/− mice compared with cPLA₂α^+/− mice, which indicates that cPLA₂α plays a role in the effector phase of EAE. Additionally, MOG-specific T cells from cPLA₂α^−/− mice, transferred into WT mice, induced EAE with delayed onset and lower severity compared with EAE that was induced by control cells; this indicates that cPLA₂α also plays a role in the induction phase of EAE. MOG-specific T cells from cPLA₂α^−/− mice were deficient in production of Th1-type cytokines. Consistent with this deficiency, in vivo administration of IL-12 rendered cPLA₂α^−/− mice susceptible to EAE. Our data indicate that cPLA₂α plays an important role in EAE development and facilitates differentiation of T cells toward the Th1 phenotype.