 Prediction of drug treatment response based on variation in genetic make up is a rapidly growing area. However, few studies examined the association between single nucleotide polymorphisms and drug response in bipolar disorder. The design of this study offers a unique opportunity to examine genetic predictors of drug response. Interestingly, a single nucleotide polymorphism at nucleotide196 GA in the human BDNF gene at codon 66 Val66Met have been reported to be associated with a predisposition to BD in family-based studies Rybakowski et al 2006, Green et al 2006. In humans, this polymorphism produces a valine - to - methionine substitution in the proBDNF protein and reduces the trafficking and secretion of BDNF protein. This is relevant because it has been estimated that 20-30 of the human population is heterozygous for the Met polymorphism of BDNF. Furthermore, there are consistent findings in BD regarding the association of Val66Met polymorphism of BDNF gene with prefrontal cognitive impairment, which was recently confirmed in a large sample of bipolar subjects Rybakowski et al 2006. In addition, crosssectional studies showed that the polymorphism of BDNF gene Val66Met was associated with response to lithium prophylaxis, but findings were not universal Rybakowski et al 2005, Masui et al 2006. However, there is a need for prospective studies in order to confirm these findings. It is possible that a single polymorphism of BDNF gene would have a negative impact of BDNF levels and, consequently, a negative impact in the response to treatment. 