Metallothioneins are intracellular proteins binding metals. There proteins are involved in zinc and copper homeostasis as well as in organism detoxication of heavy metals. The induction of metallothioneins synthesis is caused not only by metal ions but also by the interleukins, by tumor necrosis factor and by glicocortycoids or the stressing factors. Metallothioneins prove the protective action in cadmium toxication and prevent interaction of cadmium with thiol groups -SH proteins. In neoplasms the increase of metallothionein level occurs both in tumors and in liver, the level of these proteins is correlated with the size of the tumor.