Objective: Bipolar affective disorder (BAD) is a common disease. The physiopatholgical factors that cause BAD are not clear. It was recently hypothesized that the disordered oxidative factors have role in the ethiology. Nitric oxide (NO), which is synthesized by nitric oxide synthetase, is found both in central and periferic nervous system. NO acts as an free oxygen radical and a neuro-transmitter. It is estimated that NO has a role in the pathophysiology of many neuropsychiatric disease including bipolar affective disorder. Arginase is mainly located in the liver and cathalizes urea synthesis. This enzyme cathalizes L-arginine which is also used for NO synthesis.