Administration of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) to rats produced a dose-dependent hypothermia. Pretreatment with the receptor antagonist methiothepin abolished this effect, and pretreatment with haloperidol, propranolol and pindolol partially attenuated it, although methiothepin and pindolol had hyperthermic actions of their own. Other receptor antagonists including ritanserin, naloxone, clonidine, phenoxybenzamine and metergoline did not significantly modify the response elicited by subsequent 8-OH-DPAT challenge. In antidepressant studies, chronic treatment (22 days) with clorgyline attenuated the hypothermic response to 8-OH-DPAT, whereas similar duration of treatment with the tricyclics clomipramine and imipramine did not significantly modify it. Also, acute treatment for three days with each of the antidepressants did not modify 8-OH-DPAT-induced hypothermia. We conclude that rat rectal temperature can be a useful model to help assess the functional state of serotonergic mechanisms, including the adaptational changes induced by long-term antidepressant treatment.