Chronic (10 days)administration of the atypical antipsychotic quetiapine (3.75 mg/kg) induced significant suppression of the IgM immune response in mice with aggressive behavior formed as a result of prolonged (14 days in CBA mice, 20 days in C57BL/6J mice) confrontations and in animals with unaltered psychoemotional status. The immunosuppressive action of quetiapine was independent of the genotype of the mice and the route (i.p. or p.o.) and scheme (single or repeated) of administration. Possible serotonin (5-HT) and dopamine (DA) receptor mechanisms of the immunomodulatory effects of quetiapine are discussed.