[show abstract][hide abstract] ABSTRACT: Accumulating evidence suggests that reduced levels of brain-derived neurotrophic factor (BDNF) in acute mood episodes may play an important role in the pathophysiology of bipolar disorder (BD). In order to assess changes in BDNF serum levels in BD patients before and after treatment for acute mania, ten bipolar patients were prospectively examined at inpatient unit admission and discharge. Diagnoses were made using the Structured Clinical Interview for DSM-IV, SCID-I. Serum BDNF levels were measured by sandwich ELISA. The results showed that BDNF levels were decreased in BD patients during mania when compared to controls (p=0.013) but this difference was no longer significant after treatment (p=0.126). A sharp increase in BDNF levels was found after treatment of the episode of acute mania (p=0.010). These findings suggest that the changes in BDNF serum levels may be associated with treatment response in acute mania. Further studies designed to validate the use of BDNF as a marker of treatment response in bipolar disorder are warranted.