The main function of emesis is to remove toxins from the body. The emetic response will also be triggered by cancer chemotherapy and radiotherapy or surgery under general anaesthesia. The mechanism of activation of the vomiting system is dependent on stimulation of gastrointestinal (mechanoreceptors and chemoreceptors) and/or central pathways which activate the chemoreceptor trigger zone in the area postrema. Postoperative emesis is activated by a range of factors before, during and after anaesthesia. The precise mechanism of action of any one of the influencing factors can only be speculated as there has been very little basic research into this area, due largely to the lack of an appropriate model for postoperative nausea and vomiting. The range of agents used in the prevention and treatment of emesis are effective to varying degrees, but some are associated with poor side effect profiles making them particularly unsuitable for prophylactic use. Newer antiemetics, which selectively antagonise 5-HT3 receptors, have proved effective and well tolerated in the treatment of chemotherapy-induced emesis and postoperative nausea and vomiting.