Thermoreceptors are of several types. Those in the hypothalamus, spinal cord, and gut apparently monitor body temperature and are involved in autonomic functions. Those in the skin, the cutaneous temperature receptors, mediate localized and general temperature sensations in humans and participate in the autonomic processes achieving endothermy in mammals and birds and in behavioral thermoregulation in submammalian species. The sensory receptors that transduce maintained and transient skin temperatures are defined by their exclusive or low threshold excitation by cold or warm stimuli. The impulse frequency recorded from a thermoreceptor afferent is consistently related to maintained skin temperature and is transiently altered by changing skin temperature. Threshold and sensitivity are comparable to those psychophysically determined in human subjects and established in studies of animal behavior. Other receptors are affected by temperature, particularly the slowly adapting mechanoreceptors, and it is still unclear whether they are also involved in either perception of heat and cold or processing of thermal information.