The mechanisms underlying the hypothermic effect of ethanol have been investigated in rats. At an ambient temperature of 26 degrees C, at which tail skin blood flow will normally be expected to play a role in regulating core temperature, no change in tail cutaneous temperature occurred during the period in which the core temperature was falling after administration of ethanol. As the drug effect waned tail skin temperature fell below the initial temperature as the hypothermia was corrected. This last observation confirms earlier results indicating a shift in the thermoregulatory set point after administration of ethanol. There was no significant change in oxygen consumption related to the ethanol induced fall in core temperature so decreased heat production would not appear to be a factor in the thermal imbalance. Neither was there any change in respiratory rate or minute volume to account for an increase in convective or evaporative heat loss via the lungs. From these results it is not clear by what mechanism the ethanol induced lowering of the set point leads to a fall in core temperature. Other avenues of heat loss, for example from other cutaneous surfaces, and further detailed thermal balance studies will be needed to resolve this problem.