Reactive oxygen species are known to contribute to tissue damage during injury and inflammation. However, these species can also be sensed by the cells and trigger intracellular signaling cascades. This review examines recent evidence on the involvement of reactive oxygen species in lipid signaling. Attention is focused on activation of phospholipase A 2 s, enzymes whose action on membrane phospholipids can also render molecules with opposite effects on cells. The participation of Ca 2+ -dependent and Ca 2+ -independent phospholipase A 2 s in arachidonic acid mobilization from phospholipids is discussed, with particular attention to the interplay between cytosolic and secreted Ca 2+ -dependent forms. The involvement of alternative routes for arachidonic acid mobilization under oxidative stress is also considered.