Fever may be defined as any abnormal elevation in body temperature. Although abnormal elevation of body temperature is sometimes a reflection of normal physiological processes, such as exercise, consumption of food, menstruation, and pregnancy,1 it is properly designated as fever only when it is a manifestation of disease. The investigations of Wunderlich2 first placed clinical thermometry on a firm basis, and his findings formed the nucleus of a large body of empiric knowledge concerning fever as a manifestation of disease. Despite the fact that much is known about fever from the clinical point of view, the mechanisms responsible for this important physiological disturbance are poorly understood. It is the purpose of this report to summarize the results of experimental studies on the pathogenesis of fever. Relationship of Fever to Tissue Injury Many widely diversified pathological entities are associated with fever. Among these are infections; "collagen-vascular diseases," such as