Melatonin occurs naturally in human organism, and its basic and the best investigated function is stabilization of biological rhythms, mainly day-night cycle. Properties very profitable for organisms, this hormone owes to its great ability of free radical scavenging and antioxidant activity. Connection between melatonin and elements occurring in human organism can be based on various relationships. Calcium ions play active role in melatonin biosynthesis, and sodium and potassium ions, thank to their properties of membranes polarization, influence melatonin penetrating possibility into cells, where this active molecule can exerts its physiologic functions. Another type of relationship exists between melatonin and zinc ions. Genomic action of melatonin appears in its ability to stimulate antioxidant genes expression, and its direct cellular action appears in increasing of these enzymes activity, among which very important place takes zinc-enzyme-superoxide dismutase (SOD). Melatonin also prevents poisoning by such elements like chromium (III) and (VI), iron and copper, through levelling toxic actions of these ions on organism. The role of melatonin in these processes relies mainly on scavenging of arisen free radicals, detoxification of hydrogen peroxide and combining excess of toxic ions into compounds harmless for organism.