Proteins, including immunoglobulins, can be modified by oxidation. Extensive oxidation of immunoglobulins leads to denaturation and loss of biological activity, while initial steps of oxidation may change their specificity due to chemical alteration of the paratope. Electro-oxidation of the IgG fraction from healthy persons progress to auto-immunoreactivity, as shown for several autoantibodies including anti-beta2-glycoprotein I. Changes in immunoreactivity of IgG due to oxidative reactions highly depend on electric current and levels of serum antioxidants. Autoimmune reactions, leading to certain autoimmune diseases, may be partially a consequence of unbalanced antioxidative status of an individual.