Atypical neuroleptics produce fewer extrapyramidal side-effects (EPS) than typical neuroleptics. The pharmacological profile of atypical neuroleptics is that they have equivalent or higher antagonist affinity for 5-HT2 than for dopamine D2 receptors. Our aim was to identify which 5-HT2 receptor contributed to the atypical profile. Catalepsy was defined as rats remaining immobile over a horizontal metal bar for at least 30 s, 90 min after dosing. Radioligand binding assays were carried out with homogenates of human recombinant 5-HT2A, 5-HT2B and 5-HT2C receptors expressed in Human Embryo Kidney (HEK293) cells. Haloperidol (1.13 mg kg(-1) i.p.) induced catalepsy in all experiments. The selective 5-HT2C/2B receptor antagonist, SB-228357 (0.32-10 mg kg(-1) p.o.) significantly reversed haloperidol-induced catalepsy whereas the 5-HT2A and 5-HT2B receptor antagonists, MDL-100907 (0.003-0.1 mg kg(-1) p.o.) and SB-215505 (0.1-3.2 mg kg(-1) p.o.) respectively did not reverse haloperidol-induced catalepsy. The data suggest a role for 5-HT2C receptors in the anticataleptic action of SB-228357.