Introduction: Genetic factors may influence response to antipsychotic treatment in patients with schizophrenia. The synaptosomal-associated protein of 25 kDa (SNAP-25) gene may be an interesting candidate gene regarding clinical outcome with antipsychotics. SNAP-25 is a presynaptic plasma membrane protein and an integral component of the vesicle docking and fusion machinery mediating secretion of neurotransmitters (1). Muller et al. reported that Mu1I T/G, Tail T/C polymorphisms in the SNAP-25 gene were associated with both antipsychotic drug response and drug induced weight gain (3). We aimed to evaluate the association of SNAP-25 (Mn1I T/G and Ddell T/C) polymorphisms with response to olanzapine in our study.