We studied the effects of melatonin on the status of immune organs and parameters of lipid metabolism in rats with alimentary obesity and parameters of lipid metabolism and immune status in Wistar rats kept on high-fat diet and receiving melatonin solution per os. Melatonin leveled the changes in blood and liver parameters of lipid metabolism, which was paralleled by normalization of cellular composition of immune organs. We conclude that melatonin can be a promising agent for the treatment of lipid metabolism and immune status disorders in alimentary obesity.