Nausea and Vomiting is usually produced by chemotherapeutic agents by releasing serotonin from the enterochromaffin cells of the small intestine.The released serotonin (5-HT) then activates 5-HT3 receptors located on vagal afferents to initiate the vomiting reflex. Postoperative nausea and vomiting is influenced by multiple patient, surgical and anesthesia related factors and is triggered by release of serotonin (5-HT) in a cascade of neuronal events involving both the central nervous system and the gastrointestinal tract. The 5-HT3 receptor has been demonstrated to selectively participate in the emetic response. Palonosetron is a 5-HT3 receptor antagonist with a strong binding affinity for this receptor and little or no affinity for other receptors. So by binding with this receptor palonosetron inhibits binding of serotonine to this receptor and also inhibits vomiting reflux.