In this review it has been speculated that PONV is induced by the anaesthetic and by the trauma and perturbations associated with surgery. Indeed, it is unlikely that PONV is caused by any one pathophysiological input, but is multifactorial in origin. These perturbations may be peripheral, central, or both, and involve direct effects on the vomiting system together with afferent inputs in the vagal, splanchnic and trigeminal nerves. A proposed scheme summarizing these inputs is given in figure 1. The precise mechanisms through which 5-HT and 5-HT3 receptors contribute to the control of PONV is unknown, but their involvement is demonstrated by the antiemetic effect of ondansetron.