The metallothionein (MT) is low molecular weight, intracellular and cysteine-rich proteins presenting high affinity for metal ions. Although the members of this family were discovered nearly 40 years ago, their functional significance remains obscure. MTs are involved in many pathophysiological processes such as metal ion homeostasis and detoxification, protection against oxidative damage, cell proliferation and apoptosis, chemoresistance and radiotherapy resistance. MT isoforms have been shown to be involved in several aspects of the carcinogenic process, cancer development and progression. MT expression has been implicated as a transient response to any form of stress or injury providing cytoprotective action. Although MT participates in the carcinogenic process and is used as a potential marker of tumor differentiation or cell proliferation, or as a predictor of poor prognosis remains unclear. Electrochemical measurements were performed with AUTOLAB Analyser (EcoChemie, Netherlands) connected to VA-Stand 663 (Metrohm, Switzerland), using a standard cell with three electrodes. The working electrode was a hanging mercury drop electrode (HMDE). The reference electrode was an Ag/AgCl/3M KCl electrode and the auxiliary electrode was a graphite electrode. MT in very low volumes was analysed by chronopotentiometric stripping analysis (CPSA). The best sensitivity of the MT determination was obtained with CPSA producing at highly negative potentials (about 1.7 V) a well developed peak H due to catalytic hydrogen evolution. The highest peak H was obtained in borate buffer of pH 7.6 in the oxygen presence. In this medium sub-femtomole of MT were detectable (0.3 fmol). The calibration curve was linear (R2 = 0.994) in tested concentration range 130 pM 6 nM MT with relative standard deviation about 5 %. Furthermore we used the optimized CPSA method for the MT determination in body tissues and obtained results are in good agreement with commonly used detection techniques (ELISA, RIA). Next we aimed on study interactions of MT with heavy metals (uptake by foodstuffs or drugs) because of heavy metals presented in organisms are immediately bounded by MT. In vitro interactions between heavy metal and MT are studied by CPSA method. It clearly follows from our results that CPSA method is very suitable for observation of the interactions between MT and heavy metals. Considerable decrease of MT CPSA signal at 50 mM CoCl2 was observed. On the base of our results, CPSA method is a new suitable tool for study MT in clinical laboratory medicine.