Abstract <p>The thermoregulatory system is the youngest homeostatic system of the organism in evolution. For its functioning, it uses almost all previously formed organs and tissues, including the mediator systems of the brain. One of these systems is the serotonergic one. It includes the neurons which synthesize, accumulate, release the mediator into the synaptic cleft or intercellular space in response to a nerve impulse, and catabolize serotonin, as well as the numerous receptors of this mediator. The review provides data about the changes in different part of the serotonergic system which take place in response to changes of the environmental temperature, as well as about the changes in the serotonergic system that affect the temperature balance of the body. The methods used by researchers to clarify the role of the serotonergic system in the body are very diverse. They include mechanical (for example, destruction of brain structures), electrophysiological, and pharmacological influences on various elements of serotonin metabolism. In recent decades, molecular genetic methods were added to the arsenal, allowing the creation of organisms with altered characteristics of the serotonergic system. It has been shown that manipulations with various components of the serotonergic system have a significant effect on the ability of warm-blooded animals to maintain body temperature, modulating both the processes of temperature information transmission and the reactions of heat production (shivering and nonshivering thermogenesis) and heat loss. However, it should be emphasized that the registration of the entire spectrum of physiological reactions aimed at maintaining the body’s temperature balance after influences on some parts of the serotonergic system has not always been carried out. And this opens the broadest prospects for research in this area.</p>