Endogenous oxidation reactions are essential for the normal biochemistry of life and are especially critical for leukocyte microbial killing mechanisms in host defense to infectious diseases. However, reactive oxidative intermediates can damage normal tissues unless kept under antioxidant control. Three selected examples of oxidant-antioxidant systems involved in infectious diseases are discussed, regulation of molecular iron catalyzed oxidations, superoxide scavengers and inhibitors of nitric oxide synthase in septic shock, and the use of glutathione replacement therapy in HIV infection and AIDS. The data suggest that antioxidants, and therapy based on increasing antioxidant potential, have a major impact on clinical infectious diseases.