We describe the pathogenesis and the typical clinical and laboratory features of the hyperthermia syndromes that may develop during neuroleptic drug treatment, environmental exposure or following the use of inhalational anesthetics. Since the features are similar and confusion is possible we emphasize the need for prompt diagnosis so that appropriate treatment, can be started without delay. Hyperthermic reactions have common pathophysiological mechanisms and they may be seen as an abnormal individual response to organic and functional stressors.