Laboratory medicine lacks the tools necessary to define appropriate test use; nonetheless, existing laboratory test characteristics, although inadequate, provide a common starting point for developing definitions of appropriate test use. As Lundberg , Szczepura , and van Walraven and Naylor  have emphasized, developing a process for defining appropriate laboratory use should receive a high priority. There is a particular need to develop methods for standardizing studies . Laboratory medicine does not, however, lack the tools necessary to change test use. Although past interventions were largely ineffective, there is growing evidence that test use can be changed by use of a variety of approaches. By using the existing tools there is much that can be done to change inappropriate test use, such as minimizing redundant testing or the use of tests that have no clinical relevance. The real opportunities will come when there are scientifically and medically sound definitions of appropriate test use that can be used to change test use and improve patient care in a cost-effective way.