Current diagnosis of depression depends on its clinical symptoms and signs, not on the results of any laboratory examinations. Establishing biological markers for diagnosis and treatment of depression is one of the most important problems to be solved in psychiatry practice. Near infrared spectroscopy(NIRS) is one of the recently developed methodologies, and can measure cerebral blood volumes simultaneously in multiple points with high time resolution. Multi-channel NIRS machines for clinical use have recently been developed by two medical companies in Japan. Authors presented the preliminary NIRS data showing that depression is characterized by decrease in cerebral blood volume activation during a word fluency task, and discussed their possible availability for diagnosis of depression.