Insufficient elimination of free radicals can induce a number of harmful effects including a damage of important molecules, injury of genetic information and failure of the control and regulatory processes, and even may contribute to malignancy. Free radicals probably participate in various respiratory diseases (e.g. adult respiratory distress syndrome, chronic obstructive pulmonary disease, chronic bronchitis, asthma). Antioxidants, as substances neutralizing effect of free radical, contribute to the protection of organism. Both many exogenous substances, e.g. enzymes, and exogenous substances, e.g. vitamins and some medicaments, have antioxidant properties. An efficacious supplementation is conditioned by an appropriate knowledge of health state and of needs of organism and also by understanding of the oxidative-antioxidative system and its equilibrium.