Appreciable phospholipase A2 activity was detected in a hind paw homogenate from rats with adjuvant arthritis or carrageenan-induced edema. The activity was neutralized by treatment with antibody raised against rat platelet secretory phospholipase A2, indicating that 14-kDa group II phospholipase A2 was induced in the hind paw during the process of inflammation. Injection of purified rat platelet phospholipase A2 into the hind paw of rats with adjuvant-induced arthritis resulted in exacerbation of edema in a dose-dependent manner, whereas no effect was observed on either normal rats or animals with carrageenan-induced edema under the same experimental conditions. These results suggest the importance of mammalian group II phospholipase A2 in the pathogenesis of some types of inflammation.