 The hypothesis for this project is that those patients who have a good response to treatment are the same ones who show the greater increase in BDNF levels earlier in the course of treatment, and who are less likely to present a polymorphism of BDNF gene. Given this context, we aim to investigate BDNF levels prospectively in patients with BD, before, during and after the treatment with quetiapine and compare measures with response to treatment, as indicated by remission in symptoms. We also aim to investigate the polymorphism of BDNF gene Val66Met and its correlation with BDNF serum levels and treatment response. 