Pathogenic organism can be considered as pro-oxidant agents because they produce cell death and tissue damage. In addition organism can be eliminated by specific cell defense mechanism which utilize in part, reactive oxygen radicals formed by oxidative stress responses. The cause of the necessarily defense process results in cell damage thereby leading to development of inflammation, a characteristic oxidative stress situation. This fact shows the duality of oxidative stress in infections and inflammation: oxygen free radicals protect against microorganism attack and can produce tissue damage during this protection to trigger inflammation. Iron, a transition metal which participates generating oxygen free radicals, displays also this duality in infection. We suggest also that different infectious pathologies, such as sickle cell anemia/malaria and AIDS, may display in part this duality. In addition, it should be noted that oxidative damage observed in infectious diseases is mostly due the inflammatory response than to the oxidative potential of the pathogenic agent, this last point is exemplified in cases of respiratory distress and in glomerulonephritis. This review analyzes these controversial facts of infectious pathology in relation with oxidative stress.