Abstract <p>Melatonin, a hormone synthesized by the pineal gland in thedark, regulates circadian and seasonal changes in metabolism, reproductionand behavior. Lots of experimental studies have been conducted to dateto explore the effects of exogenous melatonin in various behavioraltests in rats. This work was aimed to carry out a meta-analysisof melatonin effects on the behavior of rats kept in standard conditions.We selected 57 publications analyzing melatonin monotherapy in differentbehavioral tests: 35 in the open field (OF), 23 in the elevatedplus maze (EPM), 12 in the forced swim (FS) test, and 21 in theMorris water maze (MWM). The meta-analysis showed that a singleperipheral low-dose (≤ 1 mg/kg/day) administration of melatoninincreases the locomotor activity of rats in the OF test. Long-term melatoninadministration also promoted an increase in the locomotor activityof rats. Melatonin has an anxiolytic effect, as evidenced by anincrease in total time rats spent in the center of the OF arenaand in the EPM open arms. A reduction in the immobilization periodin the FS test suggests an antidepressant effect of the hormone.The anxiolytic and antidepressant effects were more pronounced infemales than in males. No convincing evidence for the effect ofmelatonin dose on its anxiolytic and antidepressant effects wasobtained. Melatonin therapy revealed an upward tendency in the timerats spent to find the platform in the MWM. Since in most studiesinvolved in the analysis, melatonin was administered intraperitoneallyand the animals were tested at a young age, we could not correctlyassess the dependence of melatonin effects on different routes ofits administration and rat age.</p>