Increased metabolism due to hyperthyroidism leads to the dysfunction of the mitochondria respiratory chain, resulting in elevated formation of the reactive oxygen species in the course of Graves-Basedov disease. It has also been reported that excessive thyroid hormone level may induce oxidative tissue injury. Furthermore, Graves-Basedow disease is frequently associated with changes of the antioxidant defence system activity. The disturbed balance between oxidative and antioxidative processes may be of significant importance in the pathogenesis of Graves-Basedow disease.