Role of preoptic area (POA) in thermoregulation is suggested by many studies. Thermosensitive POA neurons receives and integrates local and afferent thermal information from peripheral thermoreceptors(1). Thermoregulatory responses are exercised by its neural connections with brainstem thermoefferent structures and target tissues. Many endogenous substances affect thermoregulation by altering activity of the POA thermosensitive neurons. Microinjection and microdialysis studies reveal the role of different neurotransmitters in the POA regulating body temperature. Presence of excitatory neurotransmitter, glutamate at the POA is known(2). Its role in many physiological functions has been reported (3,4). However, role of glutamate per se on thermoregulation is not reported in awake rats. The present study was done as per the guidelines of the Institutional Animal Ethics, AIIMS and Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA). Under sodium pentobarbitone anesthesia (40mg/kg BW,i.p), 14 adult male Wistar rats (8 glutamate injected, 6 saline injected) were implanted with a K-type thermocouple at hypothalamus(5) and peritoneal transmitter to record brain and body temperature (Tbr, Tb) respectively. Voveron (0.1mg/kg BW) was given to reduce pain during post-operative recovery. Gentamicin (40 mg/kg BW,i.m) was given as antibiotic for 3days. Effect of intrapreoptic microinjection of glutamate (20ng/200nl) on Tb, Tbr (2h prior and 4h post-injection) was studied after 10 days of post-surgical recovery. Microinjection site was confirmed histologically. Tb and Tbr are expressed as mean±SD. There was a constant rise in Tb ranging from 38.3±0.7°C to 38.8±0.3°C which spanned the total post-injection recording period and the maximum Tb was 39.0±0.5°C. There was also rise in Tbr during the post-injection recording period, ranging from 38.6±0.3°C to 38.9±0.2°C and the maximum Tbr was 39.0±0.1°C. At each time-point (15 min interval), 4 h post-injection data of glutamate and saline was compared with the corresponding time-matched control data using independent sample T-test. It was found that glutamate microinjection led to significant increase in Tb and Tbr at all time-points (p<0.05, p<0.005, p<0.001). During most of the post-injection time of hyperthermia, rats maintained curled up posture with pilorection and immobility. Whereas, maximum rise in Tb and Tbr after saline microinjection was 37.9±0.3°C and 37.7±0.2°C respectively, which was significantly lower than the hyperthermia, observed after glutamate microinjection. Moreover, hyperthermia due to glutamate was decreased by intraperitoneal injection of propranalol, indicating involvement of brown adipose tissue thermogenesis. We propose that glutamate in the POA participate in both heat production and conservation mechanisms.