The effect of TFMPP, an agonist of the 5-HT1b receptors, was studied in mice on several psychopharmacological parameters. In contrast to imipramine-like drugs, TFMPP neither antagonized reserpine-induced hypothermia nor increased yohimbine-induced toxicity. Similarly to imipramine-like drugs, TFMPP antagonized oxotremorine-induced hypothermia and was active in the behavioural despair test. In addition, TFMPP normalized a social behavioural deficit induced by isolation. The effects of TFMPP on oxotremorine-induced hypothermia in the behavioural despair test and in the isolation-induced social behavioural deficit are all antagonized by d-1 propranolol. It is concluded that TFMPP seems to possess psychotropic activity resembling only in part that of imipramine-like drugs and that these actions may be mediated through 5-HT1b receptors.