S100B, an acknowledged marker of brain damage, is increased post-traumatically in plasma. The aim of this study was to investigate the diagnostic value of S100B release in experimental local extracranial ischemia and reperfusion. Anesthetized rats underwent laparotomy and ligation of the afferent blood vessels to the liver, gut, or kidney to achieve local ischemia in each organ separately. After 60 min of ischemia, ligatures were removed and resuscitation was performed for 3 h. S100B was determined in plasma by immunoluminometric assay 55, 65, and 240 min after the onset of ischemia (5 min before reperfusion and 5 min and 3 h after the onset of reperfusion). During ischemia of the liver, S100B increased before ligature removal and reperfusion, reaching significance early after the onset of reperfusion and remaining almost unchanged throughout reperfusion. In contrast, S100B did not increase during ischemia of the gut or kidney before ligature removal or during early reperfusion but increased significantly to similar levels as during reperfusion of the liver 240 min after the onset of ischemia (after 3 h of reperfusion). Our findings show for the first time that S100B increases during local extracranial ischemia and reperfusion. These experimental findings support the concept that brain damage is not necessarily the cause of increased S100B. Although S100B has been an acknowledged marker of brain damage for years, our experimental clinically relevant data indicate that S100B is, in fact, not specific as a marker of brain damage in the setting of local ischemia and reperfusion of the liver, gut, and kidney because local ischemia and reperfusion of these organs cause an S100B increase per se.