Lesopitron acts as a ligand for central serotonin 5-HT1A receptors. Ki obtained from [3H]8-OH-DPAT competition studies was 104.8 +/- 10.6 nmol/l. As lesopitron did not affect the binding of [3H]paroxetine, involvement of the serotonin reuptake system in the effects of lesopitron is rejected. Lesopitron inhibits haloperidol-induced catalepsy that is the consequence of its action on 5-HT1A autoreceptors. The ability of lesopitron to induce 5-HT syndrome reflects post-synaptic 5-HT1A receptor activation and the reversion of 8-OHDPAT-induced 5-HT syndrome by lesopitron suggests a partial agonist effect on this receptor-type. Lesopitron induced a hypothermic effect due to the enhanced activation of post-synaptic 5-HT1A receptors. The agonist effect of lesopitron on 5-HT1A receptors and its marked hypothermic effect is an added value for this drug and a stimulus to the study of its possible neuroprotective action.