Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family, and enhances the growth and maintenance of several neuronal systems. In addition, BDNF may promote neurogenesis and protect against hippocampal volume loss in depressive disorders. Although first detected in brain, BDNF also exists in peripheral tissues and is mainly stored in platelets and circulates in blood. Recent reports indicate that serum BDNF levels in depressive patients are lower than in control subjects, and antidepressant treatment increases serum BDNF levels in responders. A single report suggests that decreased serum BDNF in major depression is related to mechanisms of platelet BDNF release; however, the mechanisms of changes in BDNF blood levels are still poorly understood. In the present study, we investigated the direct influence of antidepressants on BDNF release from platelets and their effects on serum levels. We used samples of washed platelets prepared from rat blood, and investigated the platelet BDNF release and serum BDNF concentration changes in response to adding antidepressants. We found that BDNF was dose-dependently released from platelets by direct treatment with various kinds of antidepressants in vitro, and serum BDNF concentration was also increased by intravenous antidepressant treatment. These results confirm that BDNF release from platelets is affected by antidepressants, which may relate to the circulating BDNF level change in peripheral blood. The response of BDNF release differs depending on the type and amount of antidepressants, making BDNF a serious candidate as a predictor of antidepressant treatment response.