In human subjects at rest changes in heart rate pulmonary ventilation, tidal volume, respiratory rate, and end-tidal carbon dioxide tension were examined at increases in deep body temperature of 1 degrees C and 2 degrees C. Each of these latter target temperatures was achieved at two different rates of temperature increase. The increase in deep body temperature was associated with a rise in heart rate and tidal volume and a reduction in respiratory rate. An increase in pulmonary ventilation associated with a reduction in end-tidal carbon dioxide tension occurred only when deep body temperature increase reached 1.5 degrees C. The apparently greater change in both pulmonary ventilation and end-tidal carbon dioxide tension during the more rapid increase in deep body temperature by 2 degrees C was not significant.