When mammalian phagocytes encounter appropriate stimuli, highly reactive oxygen derived free radicals (superoxide and hydroxyl) and related species (hydrogen peroxide and hypochlorous acid) may be produced as a normal mechanism in the defence of the host against invading microorganisms. The radicals are destructive to most biological molecules and are responsible for much of the damage inflicted by phagocytes on both microorganisms and surrounding tissues at sites of infection or inflammation. Increasing evidence suggests that the generation of oxygen metabolites plays an important role not only for perpetuation of chronic inflammation, but also for the etiology of other health problems i.e. ageing, cancer, ischemia, and radiationinduced injuries. The extent of tissue damage in inflammation may partly be the result of the balance between free radicals generated and the antioxidant/radical scavenger protective defence systems. The implication of oxygen free radicals in inflammation and future directions are briefly discussed in the present overview.