We studied the consequence of taurine release within the supraoptic nucleus (SON) for the hormonal stress response. Rats were chronically implanted with both microdialysis probes in the SON and jugular venous catheters. Three days later the animals received either Ringer's solution or a specific taurine antagonist via retrodialysis directly into the SON during a 10-min forced swimming session, while simultaneously blood samples were collected. Compared to the Ringer's control, treatment with the taurine antagonist significantly attenuated the increase in plasma corticotropin concentration caused by the stressor exposure (P < 0.05, analysis of variance). This finding supports the hypothesis that the hypothalamic-neurohypophysial system is a potent regulator of the hormonal stress response and suggests an important role for taurine in this context.