Although body temperature has been monitored for more than a century as a means of distinguishing health from disease, physicians' perceptions of concepts of clinical thermometry are largely unknown. To characterize such perceptions, we did a descriptive analysis of responses to a survey questionnaire dealing with body temperature. Seventy-five percent of the 268 physicians and physicians-in-training surveyed offered 37 degrees C (98.6 degrees F) as their definition of "normal body temperature." Only 10 (4%) specified a particular body site (eg, oral or rectal) of temperature measurements in their definition. Although 98% believed that body temperature normally varies during the day, there was not a consensus as to the magnitude of such variability. There was also considerable disagreement as to the specific temperatures defining the lower and upper limits of the febrile range. Subjects exhibited a clear preference for the Fahrenheit scale in their responses. Medical students differed significantly from graduate physicians in several of the areas examined.