Cool question: warm reply.

To the Editor. —In the Questions and Answers section of the January 15,1992, issue of The Journal , 1 a physician asks if a subgroup of persons exists whose temperature, in the absence of illness, never exceeds 97°F (36.1°C) but who have a fever when their temperature exceeds 99°F (37.2°C), and during a febrile illness, have temperatures that never exceed 100°F (37.8°C). In his answer, Hirschmann 1 described temperature variations in healthy persons indicating that temperatures below 98.6°F (37.0°C) are common. Hirschmann's lowest oral temperatures ranged between 97.5°F (36.4°C) and 97.8°F (36.6°C). 1 But these are not the low normal temperatures of "naturally hypothermic" persons. Petersdorf and Root 2 report that in healthy individuals, oral temperatures may be as low as 96.5°F (35.8°C). They found that oral temperatures of 97°F (36.1°C) are not uncommon on awakening, and that lowest diurnal temperatures occur between 2 AM and 4 AM. Temperatures peak at