There is considerable evidence that schizophrenia is associated with immune system dysregulation. For example, blood and cerebrospinal fluid (CSF) levels of proinflammatory cytokines are significantly increased in schizophrenic patients, and their normalization correlates with improvement in psychotic symptoms. In fact, typical and atypical antipsychotics are reported to modulate immune function in in vitro and in vivo studies. In the present study, we examined the anti-inflammatory effect of antipsychotics, clozapine, olanzapine, risperidone and haloperidol, on serum cytokine levels in lipopolysaccharide (LPS)-treated mice. Atypical antipsychotics, such as clozapine, olanzapine and risperidone, but not haloperidol, suppressed tumor necrosis factor (TNF)-alpha and interleukin (IL)-6, and up-regulated IL-10. Moreover, only clozapine, robustly increased the serum levels of IL-10. Clozapine reproduced its anti-inflammatory feature in polyinsinic-polycytidylic acid sodium salt (Poly[I:C])-induced inflammation. Thus, the anti-inflammatory effect of clozapine would adapt to inflammation induced by some varieties of antigens. Several receptor ligands, such as 8-OH-DPAT, ketanserin, prazosin and scopolamine, were also examined as to their anti-inflammatory effects on serum cytokine levels in LPS-treated mice. Ketanserin and prazosin, but not 8-OH-DPAT nor scopolamine, behaved similarly to atypical antipsychotics. However, the remarkable increase of serum IL-10 level observed in clozapine was not detected in ketanserin and prazosin. These results suggest the unique efficacy of atypical antipsychotics in the suppression of proinflammatory cytokines, and the increase of anti-inflammatory cytokine, IL-10.