Staphylococcal enterotoxin A (SEA) produced by Staphylococcus aureus is a major cause of symptoms of food poisoning in humans throughout the world every year. The primary symptoms are nausea, vomiting, abdominal cramping and diarrhea occurring within 1 to 4 h after ingestion of the contaminated food. In addition to causing emesis, SEA is also a member of pyrogenic superantigen family. Over the past few decades, several studies have been conducted on the nature of SEA and the molecular basis of the superantigen activities of SEA has been extensively studied. However, it remains unclear how SEA induces emesis and its emetic signal pathway. We investigated a mechanism of SEA-induced emesis using a small emetic animal model, house musk shrew. SEA-induced emesis in the animals was inhibited by a 5-hydroxytryptamine (5-HT) synthesis inhibitor and a 5-HT3 receptor antagonist. SEA increased 5-HT release in the small intestine. Pretreatment with 5,7-dihydroxytryptamine markedly inhibited SEA-induced emesis. SEA-induced emesis was also abolished by surgical vagotomy. On the other hand, cannabinoid (CB) receptor agonists inhibited SEA-induced emesis, and the action was reversed by a CB1 antagonist. Both 5-HT release and CB1 receptor expression were found in the mucosal and myenteric plexus of the intestine. Moreover, a CB1 receptor agonist significantly decreased the 5-HT release in the intestine. These results demonstrate that SEA induces 5-HT release in intestine, and that the 5-HT3 receptors on vagal afferent neurons are essential for SEA-stimulated emesis. In addition, SEA-induced emesis is down-regulated by the CB system through decreasing 5-HT release in intestine.