The effect of Clostridium perfringens epsilon toxin on rat isolated aorta was investigated. The toxin caused contraction of the isolated aorta in a dose-dependent manner. The toxin induced no contraction of the isolated aorta in low-Na medium and of the tissue stored at 4 C for 7 days. However, tetrodotoxin (TTX) had no effect on the toxin-induced contraction. The toxin-induced contraction was significantly inhibited by phentolamine and prazosin, but did not by atropine, mecamylamine, chlorpheniramine and methysergide. These data suggest that the toxin-caused contraction is mediated through nervous system in rat isolated aorta.