Abstract: Temperature "clock" was measured by 24-h continuous recordings of body(oral)and skin(middle back, postaural, elbow, hand, foot) temperature in 23healthy young adults. Experiments were undertaken under "standard ambienttemperature" (～20℃) and "thermal neutrality" (～30℃) conditions, respec-tively.The former simulated standard temperature condition during wakefulness,whereas the latter simulated the commonly "quilt" ambient temperature duringsleep. Measurements of skin temperature were done by a specially-equippedmultiple thermographic device model WMSY -01,which allowed 24-h automa- tic recordings of 10 different skin positions of the body at a glance. Resultsshowed: (1) Skin temperature of the extremities (especially foot) showed signi-ficant reversal under "thermal neutrality" temperature condition(～30℃)whichsimulated the commomly "quilt" ambient temperature during sleep. (2)A minornadir was observed around 14:00 between 10:00 and 16:00 of the temperature"clock" of both "non-siesta" and "siesta" groups, indicating the possible in-volvement of the secasemidian nature of temperature "clock" in young adultsubjects.

Key words: Human temperature "clock", skin temperature, circadian rhythm, circasemidian rhythm