**1. Introduction**

Free radicals are chemical compounds with unpaired electron(s), therefore being considered very active molecules. The cells had developed their own antioxidant defence systems in order to prevent the free radicals synthesis and to limit their toxic effects. These systems consist of enzymes which breakdown the peroxides, enzymes which bind transitional metals or compounds which are considered scavengers of the free radicals. Reactive species oxidize the biomolecules that will further elicit tissue injury and cell death. Evaluation of free radicals involvement in pathology is rather difficult due to their short life time.
