Aims: It has been hypothesized that the activation of the immune system may be involved in the neuropathological changes occurring in the central nervous system of schizophrenic patients. Cytokines play a key role in the activation of the immune system. Moreover, they strongly influence the dopaminergic, noradrenergic and serotonergic neurotransmission. To the best of our knowledge, in schizophrenic patients, plasma levels of interleukin (IL)-12 were investigated only in one study, where deregulation of IL-12 was determined. However, genotypical variations of the IL-12B (p40) gene have not been investigated for schizophrenic patients yet. Therefore, in the present study, we aimed to examine polymorphic variants of IL-12B (p40) gene promoter region in patients with schizophrenia in a population of the Elazig Region of East Anatolia, Turkey.