Melatonin, a chemical compound originating from the family of indoleamines is widely spread amongst different types of living organisms in the world. This highly evolutionarily conserved molecule exist in organisms as different as algae and humans and structurally related compounds seam to be present in all life forms. This indole derivative is synthesized by a number of cells and tissues but in vertebrae, with a special respect to mammals, melatonin is a hormone secreted by the pineal gland. It is now well established that synthesis of melatonin exhibits a circadian rhythm with maximum formation of this molecule occurring during the night. It participates in many important physiological functions including the control of seasonal reproduction as well as influences the immune system and plays an important role in regulating the circadian rhythms. Lately, it has been efficiently used as the regulating agent in the treatment of a wide variety of daily-rhythm disturbances, from common insomnia to jet-lag. Recently melatonin has been claimed by some authors to be a sort of a miraculous drug exhibiting anti-aging, life-prolonging action, a fact that has induced a "melatonin madness", effectively stimulated by media. These statements, rising unjustified hopes, are considered by many other scientists as exaggerated and "crossing the barrier of scientific objectivity". Nevertheless, systematic studies, led mainly by the group of Prof. Russel J. Reiter from the University of Texas Health Science Center, have provided convincing evidence that melatonin is a very potent antioxidant and it may be among the natural agents protecting organisms from oxygen radical damage. It is important to mention that accumulated free radical damage is one of the main factors responsible for DNA modification and carcinogenic changes in tissues influencing the rate of aging. It has been suggested that the role of melatonin in the protection against radical-induced damage is mainly based on its ability to scavenge hydroxyl radicals, considered to be the most damaging of free radicals generated in living organisms. Melatonin has been shown to scavenge also the organic oxyl and peroxyl radicals, a fact that may also contribute to the antioxidant action of this compound. Since there is still little physical and chemical evidence explaining the mechanisms by which melatonin possibly might act as the "super scavenger", the reactivity of this molecule towards various types of free radicals awaits thorough studies.

Radiation-chemical methods provide efficient tools for producing free radicals in a controlled way and then studying their fast reactions and transformations. One of such a methods is pulse radiolysis in which accelerated electrons beam is employed to induce water radiolysis and free radicals formation. Manipulating the radiolysis parameters (pH, additions of selectable scavengers, radical "converters" or radical precursors) it is possible to generate OH radicals, H atoms and hydrated electrons (primary water radiolysis products) as well as other radicals with predictable efficacy.

So far in our research we focused mainly on the determination of the rate constants of the reactions of melatonin with hydroxyl radicals and hydrated electrons, gathering data related to the nature of the intermediates formed in these reactions.