The аim of the research – to investigate the effects of melatonin on oxidative stressbiomarkers malonic dialdehyde (MDA) and oxidatively modified proteins (OMP) inblood, liver and kidneys of rats exposed to subacute alcohol intoxication, its combinationwith constant light exposure, and caffeine intake.Materials and methods. Experiments were performed on 42 male rats weighing180-200 g kept under standard conditions of vivarium and artificial equinox. Subacutealcohol intoxication was induced by intragastric administration of 40 % ethanol at a doseof 7 ml/kg of body weight for 7 days. Caffeine was administered by gavage at a doseof 30 mg/kg of body weight.Results. Ethanol poisoning results in increase in MDA and OMB, and liver was the mostaffected (90 % and 42 % higher than control). The combination of ethanol with caffeinereduced the intensity of oxidative stress in the blood but increased the toxic effectsof ethanol on the liver (MDA and OMP were 116 % and 60 % above control range).The most significant increase in MDA was in the liver and kidneys under combinationof alcohol intoxication with exposure to constant light (139 % and 33 % respectively).There was a decrease in OMB level along with elevation of MDA level in kidneys of allgroups of alcoholized animals.Administration of 5 mg/kg melatonin for 7 days limited the rise in MDA in the bloodand liver of animals and changes in OMB content in the blood liver and kidneys of animalsexposed to ethanol and constant lighting. Melatonin showed to be less effective in theliver and kidneys of rats treated with a combination of ethanol and caffeine.Conclusion. The data obtained are evidence of the pronounced antioxidant melatoninaction and its capacity to prevent toxic effects of ethanol and its combination withconstant lighting and caffeine introduction into organism.