This study investigated changes in plasma levels of the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) in decapitated mice in response to the variable stresses of restraint, restraint and water immersion, and foot shock. DOPAC levels, but not norepinephrine (NE) and epinephrine (EPI) levels, increased upon exposure to these stresses. Plasma DOPAC levels measured using the decapitation method in rats were then compared with those measured using the catheter method. The NE and EPI levels in plasma measured using the decapitation method were much higher than those using the catheter method under basal conditions. In contrast, differences in the levels of DOPAC in plasma were smaller than those of NE and EPI under basal conditions using in both methods; furthermore parallel changes in plasma DOPAC levels occurred during restraint and water immersion stresses. These results indicate that the plasma DOPAC levels measured in mice using the decapitation method were clearly increased by the different stresses. Furthermore, in rats there were correlations between the decapitation and catheter methods for plasma levels of DOPAC. Thus the change in plasma DOPAC levels measured using the decapitation method is a good indicator of stress responses involving sympathoneural activity.