Body temperature increases when individuals experience salient, emotionally significant events. There is controversy concerning the contribution of non-shivering thermogenesis in brown adipose tissue (BAT) to emotional hyperthermia. In the present study we compared BAT, core body, and brain temperature, and tail blood flow, simultaneously measured, to determine whether BAT thermogenesis contributes to emotional hyperthermia in a resident Sprague-Dawley rat when an intruder rat, either freely-moving or confined to a small cage, is suddenly introduced into the cage of the resident rat for 30 min. Introduction of the intruder rat promptly increased BAT, body and brain temperatures in the resident rat. For the caged intruder these temperature increases were 1.4±0.2, 0.8±0.1, 1.0±0.1C° respectively, with the increase in BAT temperature being significantly greater (p<0.01) than the increases in body and brain. The initial 5 min slope of the BAT temperature record (0.18±0.02C°/min) was significantly greater (p<0.01) than the corresponding value for body (0.10±0.01C°/min) and brain (0.09±0.02C°/min). Tail artery pulse amplitude fell acutely when the intruder rat was introduced, possibly contributing to the increases in body and brain temperature. Prior blockade of beta-3 adrenoceptors (SR59230A 10 mg/kg i.p.) significantly reduced the amplitude of each temperature increase. Intruder-evoked increases in BAT temperature were similar in resident rats maintained at 11°C for 3 days. In the caged intruder situation there is no bodily contact between the rats, so the stimulus is psychological rather than physical. Our study thus demonstrates that BAT thermogenesis contributes to increases in body and brain temperature occurring during emotional hyperthermia.