Flesinoxan acts as a partial agonist at postsynaptic and as a full agonist at presynaptic 5-HT1A receptors. The intravenous administration of Flesinoxan suppresses the firing activity of both CA3 pyramidal neurons and dorsal raphe 5-HT neurons. The capacity of Flesinoxan to antagonize the effect of 5-HT on CA3 pyramidal neurons was similar to that of 8-OH-DPAT. The acute brain penetration of [3H]Flesinoxan and [3H]8-OH-DPAT are determined. Nine minutes after intravenous administration, [3H]8-OH-DPAT reached significantly greater brain concentration than [3H]Flesinoxan. Subcutaneous administration of Flesinoxan and 8-OH-DPAT produce dose-dependent hypothermia. The Flesinoxan-induced hypothermia is significantly attenuated by prior administration of the non-selective 5-HT1A antagonist pindolol and the 5-HT1/2 antagonist methysergide. Similar degrees of hypothermia is achieved with 3 mg/kg of Flesinoxan and 0.5 mg/kg of 8-OH-DPAT. The maximal effect of Flesinoxan occurs 30 min later than that of 8-OH-DPAT and fades more slowly.