Metallothionein (MT) is a protein involved in numerous key processes, and the most important include zinc ion homeostasis, detoxification of heavy metals, and protection against oxidative stress. MT by interaction with other proteins fulfills its function, resulting in different effects in the body. Interaction of MT with ferritin, which causes a redox reaction, resulting in the reduction of Fe(3+) stored in ferritin and a release of harmful Fe(2+) , was observed. Referring to the redox function of MT, it has been shown that the pair of GSH/GSSG modulates transfer of Zn between MT and Zn-binding proteins. Furthermore, it was shown that GSSG, in the presence of GSH, interacts directly with MT. Apothionein-MT can retrieve Zn from the transcription factors or Zn-containing enzymes. Apothionein-MT by taking Zn can deactivate metal-dependent enzymes while Zn-MT has the opposite effect. As the effect of MT interaction with low-density lipoprotein receptors-megalin and lipoprotein receptor related protein 1, the uptake of Cd-MT occurs and results in the disruption of many functions of proximal tubules. MT is involved in numerous processes and many of them are regulated by protein-protein interactions. Possibly in the future MT will become a therapeutic agent, which will result in a breakthrough in the field of pharmacy and medicine.