Abstract. Leptin as well as gamma-aminobutyric acid (GABA) are involved in the regulation of feeding behavior and energy balance. Recent experimental data suggest involvement of GABAergic mechanisms in the regulation of body temperature. The present study determined the effect of leptin on the core body temperature in rats at ambient temperature of 22±1ºC. It has been investigated the changes of core body temperature in male Wistar rats after systemic (i.p.) administration of leptin, GABAB-agonist baclofen and GABAB-antagonist CGP35348 applied separately, as well as applied in combinations. The results suggested that systemic administration of leptin produced signifi cant hyperthermia in rats, as well as the GABAB-antagonist CGP35348, while the GABAB-agonist baclofen caused decrease in core body temperature. However, there wasn’t synergism in hyperthermic effect of leptin and GABAB-antagonist. The effect of combination was lower than the effects of substances applied alone. Neither hyperthermic effect of leptin nor hypothermic effect of GABAB-agonist occurred when leptin was applied just prior baclofen. In conclusion, there was not synergism between leptin and GABAB-antagonist or GABAB-agonist, when they were applied simultaneously.