It is hypothesized that molecular components of dopaminergic system, especially the dopamine D3 receptor gene (DRD3), may play a crucial role in the pathophysiology of schizophrenia, because it is abundant in the limbic system of the brain and it binds antipsychotic drugs. Several groups attempted to find an association between a serine-to-glycine polymorphism of the DRD3 gene (Ser9Gly) and schizophrenia; however, the results were inconsistent. In this study, we aimed to investigate the relationship of the Serine/Glycine polymorphism of the DRD3 gene with therapeutic response to clozapine treatment between Turkish schizophrenia patients (N¼92) and healthy controls (N¼100). Genotype groups were comparable in BPRS, SAPS, SANS analysis of response to clozapine. Our results suggest that an association between the Ser/Gly polymorphism ofDRD3 gene and response to clozapine in Turkish schizophrenia patients is unlikely to exist