Summary: Metallothionein is a low-molecular intracellular protein which can play animportant role in heavy metal homeostasis in living organisms. Less is known about molecular mechanisms of MT expression. Metals probably participate in MT expression by binding to transcriptional factor MTF-1. Expression of human metallothioneins (MT-1a, MT-2a) can be induced by increasing amount of heavy metals, hormones, cytokines, and/or xenobiotics. Recent studies described the important relationship between MT and carcinogenesis, spontaneous mutagenesis and anti-cancer drugs. Overexpression of metallothioneins is studied as a new prognostic marker in a number of malignant and high grading tumors.