Budgetary restraints have been used to limit the freedom of medical prescription. This paper proposes a simple approach to the evaluation of costs and benefits. First the efficacy of a new approach Is defined and compared with the best care with existing means. The Incremental gain Is then compared with the true cost of both procedures. The Innovation should be adopted only where the gain Is high and the cost low (or at least only minimally Increased). In cases of debatable gain and costs, detailed cost-benefit analysis and quality of life studies are needed. We conclude that at present, 5-HT3 receptor antagonists should only be used to control the acute phase of emesls.