A bulk of biochemical pathways, which play a crucial role in such processes as protection of cells from oxidative stress, cellular proliferation or selenium metabolism are regulated by thioredoxin - thioredoxin reductase system. This system consists of two groups of enzymatic proteins which require NADPH for their activity. NADPH is acquired mainly from pentose phosphate pathway. Proteins from thioredoxin family can be found in all organisms. Moreover, a number of viral products exploit thioredoxin - thioredoxin reductase system for their replication. It has been shown, that various splicing forms of thioredoxin may exert unique physiological functions, for instance in the regulation of the immune respon- se. Recently, a growing number of reports revealed that this system participates in several stages of carcinogenesis and can affect the outcome of standard antitumor treatments.