The biological role of the histidine-containing dipeptide carnosine (beta-alanyl-L-histidine) has been reviewed. The properties and putative biological role of the dipeptide in vertebrate tissues are considered. The antioxidative activity of carnosine and related compounds is described. The author's conception of the membranoprotective effect of carnosine on cells, tissues, and whole organism has been formulated. The properties of carnosine as an antistressory radioprotective agent are discussed. The data presented suggest that carnosine is a perspective immunomodulating tool which has many applications in medicine.