The detection of thermal asymmetry may lead to the diagnosis of significant disease states, especially those of a neoplastic or vascular nature. Estimates of acceptable thermal asymmetry have been made; thermal asymmetry has not previously been quantified in normal subjects. In 10 normal male volunteers, ages 17–38, thermal difference between symmetric areas of the chest, abdomen, and back never exceeded 1°C. Statistical treatment of these data suggests that thermal differences in excess of this in the male are abnormal.