Humans are warm-blooded mammals and must maintain a constant internal temperature. Body temperature is controlled by the hypothalamus in the brain, with input from sensory receptors throughout the body. At any given time, body temperature is a function of heat production and heat loss. Temperature-regulation problems can result in several conditions. These include fever, hyperthermia and hypothermia. EMTs and paramedics must be familiar with the physiological and pathophysiological processes resulting from these disorders. By close observation of the patient, it should be fairly easy to determine which underlying processes are causing the observed signs and symptoms. With this knowledge, you can provide competent, compassionate prehospital care.