Neurotensin-producing perikarya and fibers have been identified in the ventral tegmental area of the rat, and recent microinjection studies indicate that neurotensin may function in the ventral tegmental area to regulate body temperature. In this study, the hypothermic response produced by intraventral tegmental injection of neurotensin was shown to be dose-dependent, with a threshold dose between 0.25 and 0.75 micrograms. When fluphenazine, a dopamine receptor antagonist, was microinjected into various forebrain nuclei simultaneous with neurotensin infusion into the ventral tegmental area, it was found to block neurotensin hypothermia. In contrast, injection with fluphenazine into the nucleus accumbens, lateral septum or preoptic area did not alter the hypothermic response. Furthermore, injection with atropine, phentolamine or diphenhydramine into the diagonal band of Broca did not block neurotensin hypothermia. Neurotensin was also injected directly into the preoptic region and shown to produce hypothermia. However, concurrent infusion of fluphenazine with neurotensin into the preoptic region did not attenuate neurotensin hypothermia. These data are consistent with the postulate that neurotensin acts in the ventral tegmental area to enhance dopamine release in the diagonal band of Broca, thereby producing hypothermia. However, neurotensin-induced hypothermia occurring after injection into the preoptic area does not appear to involve dopamine systems.