Numerous studies on animal models and cell cultures confirm the role of free radicals/reactive oxygen species and oxidative damages in the process of the initiation and promotion of neoplastic diseases. Also epidemiological studies attribute an important role to disturbances in the pro- and antioxidative potential in the development of malignancies and highlight the essential function of antioxidants to protect the cells from the attack of free oxygen radicals. The current literature data on the parameters of the anti- and prooxidant status in patients with malignant diseases and their role in pathogenesis of the disease is reviewed in this article.