The receptor binding and pharmacological profile of the new, putative 5-HT1A receptor antagonist MP-3022 (4-[3-(benzotriazol-1-yl)propyl]-1-(2-methoxyphenyl)piperazine) were studied. Another 5-HT1A receptor antagonist, (S)-WAY 100135 ((S)-N-tert-butyl-3-[4-(2-methoxyphenyl)piperazine-1-yl]-2- phenylpropanamide), was used as a reference drug in functional models. MP-3022 showed a high affinity (Ki) of 25 nM and 69 nM, respectively, at 5-HT1A binding sites and alpha 1-adrenoceptors in vitro. The Ki values of MP-3022 in relation to other binding sites examined (5-HT2A, alpha 2- or beta-adrenoceptors, dopamine D1 and D2) were 20-100-fold lower. In functional studies, MP-3022 significantly attenuated the 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin)-induced decrease in the population spike evoked in the CA1 cell layer of the hippocampal slice preparation, without producing its own effects. The 8-OH-DPAT-evoked increase in the corticosterone concentration in the serum as well as the 8-OH-DPAT-mediated decrease in the 5-HT turnover in the hippocampus were attenuated by MP-3022. MP-3022 increased the serum corticosterone concentration only at the highest dose used, but it did not change the 5-HT turnover in the hippocampus. Like MP-3022, (S)-WAY 100135 antagonized the 8-OH-DPAT-induced effects. It has also been demonstrated that (S)-WAY 100135 is devoid of an intrinsic activity at 5-HT1A receptors. The data obtained demonstrate that, like (S)-WAY 100135, MP-3022 behaves like a functional antagonist at pre- and postsynaptic 5-HT1A receptors.