Objective: Activity of the paraoxonase 1 (PON1) enzyme varies prominently according to the PON1 Q192R genotype. The arginine (R) genotype hydrolyzes peroxided lipids more quickly and efficiently than the glutamine (Q) genotype. The Q phenotype suggests greater liability to neurodegenerative processes, cardiovascular and malignancy risks than the R phenotype. Stimulated PON/ARES ratio is associated with the PON1 Q192R polymorphism. This study aimes to assess the Q192R phenotype in schizophrenia, bipolar disorder and depression.