Setoperone, a piperidine derivative known for its potent serotonin and moderate dopamine receptor blocking properties was labelled with the positron emitter 18F using a nucleophilic substitution on the nitro derivative. The general pattern of the in-vivo and in-vitro rat brain distribution of this new radioligand was consistent with the mapping of serotonin (5HT2) and dopamine (D2) receptors. The cortical binding of 18F-setoperone was selectively inhibited by ketanserin and not by sulpiride. The affinity of the radiofluorinated ligand for the serotonin receptors was in the nanomolar range (Kd = 0.7 nM).