Unit activities of thermosensitive (TS) and non-TS neurons in the preoptic area (PO) of the monkey were investigated during high FR bar press (BP) tasks for seeking coor air (CT) or food (FT). The monkey pressed a bar when ambient temperature (Ta) was raised (35-42°C) and the animal was rewarded with a fall in Ta (23-25°C). The FT was guided by presentation of cue light or food and the animal was rewarded with food. Thirty-eight percent of the neurons responded to changes in PO temperature. The population of neurons which changed in firing rate during CT was higher among TS neurons than among non-TS neurons, The most frequently observed response was a sustained decrease in activity during the bar pressing and reward periods. The magnitude and duration of activity changes at the reward stage were affected by the animal's core and skin temperatures and appeared to be associated with the rewarding value of thermal stimuli. More than half of TS neurons which changed the activity during CT also showed the same type of response during FT. The results suggest that PO TS neurons are involved in the drive and/or reward mechanism of thermoregulatory behavior, and that they are also somehow related to the neural processes of non-thermal emotional behaviors, such as feeding.