The antioxidant properties of carnosine and its components histidine and beta-alanine were compared using several model systems: glutathione-horseradish peroxidase-luminol (GSH-HRP-luminol), xanthine-xanthine oxidase (X-XO), stimulated human blood polymorphonuclear leukocytes (PML), and egg yolk phospholipid liposomes in the presence of Fe2+ ions. Carnosine and histidine (30-40 mM) were shown to cause 50% suppression of free radical reactions in the GSH-HRP-luminol system, whereas beta-alanine displayed no activity. The O(2-)-scavenging activity of carnosine in the X-XO system was demonstrated; 50% inhibition was achieved at 7.1 x 10(-5) M. Suppression of the luminol-dependent PML chemiluminescence by carnosine and reduction of the latent period of the Fe(2+)-induced chemiluminescence of the liposome suspension was suggested to demonstrate its ability to interact with Ca2+ and Fe2+ ions. This was confirmed by the o-phenanthroline test. The results obtained demonstrate that carnosine is capable of scavenging different radicals and binding divalent metal ions. The antioxidant activity of carnosine was observed in all the systems studied, and carnosine effective concentrations corresponded to those found in the brain and muscles. The universal effects of carnosine and its high concentration in excitable tissues suggest this dipeptide to be an inhibitor of free radical reactions in vivo.