This study aims to see in an animal experiment how differently the low and high doses of melatonin affect the antioxidant status and peroxidation of lipids. Forty-two male Wistar-Albino rats weighing about 200 gr (180-220) aged 6-7 months were used. Of these rats, 12 were fed with normal rat chow for 12 weeks. The latter ones were divided into two groups, each containing 6 rats. Group 1 (control group) received daily intraperitoneal injections of NaCl (0.9%; w/v). Group 2 was injected ethanol daily (4%; v/v; i.p.) to see the effects of ethanol in which we dissolved melatonin. Thirty rats were fed with a diet enriched with cholesterol (2%; w/w), cholic acid (0.5%; w/w) and propilthyouracil (0.5%; w/w) for 12 weeks. These rats were divided into three groups each containing 10 rats. The low-dose group received melatonin 1 mg/kg/d; i.p. (group 3), the high-dose group received melatonin in a dose of 10 mg/kg/d; i.p. (group 4), and only the cholesterol group did not get any vehicle (group 5). Total cholesterol (TC), LDL cholesterol (LDL-C), total antioxidant capacity (TAC), oxidized LDL (oLDL) and TBARS lelvels were measured in all groups. The produced high-cholesterol diet increased LDL cholesterol. Melatonin decreased the extent of this plasma lipoprotein increase and also prevented the oxidation of it. This effect was clearer when the dose was higher. Antioxidant status seems to be also dose-dependent (Tab. 2, Ref. 33).