This research evaluated the effects of providing physicians with information about the prices of diagnostic tests on their subsequent test-ordering behavior. The study population consisted of 36 second- and third-year residents and 23 clinical faculty in three family practice centers affiliated with the Department of Family Medicine at Wayne State University School of Medicine, Detroit, Michigan. Study participants were asked to review four case studies, each describing a patient with ambiguous symptoms, and to indicate on an attached test order form the tests they would order for each patient. Subjects were randomly assigned either to a group that received test order forms on which the prices of diagnostic tests were printed (price-information group) or to a group that received test order forms with no prices indicated (control group). The study results show that for each of the four cases, the average number of diagnostic tests ordered was significantly lower in the price-information group than in the control group. Our findings also show an average reduction in the cumulative cost of tests ordered per patient of 31.1 per cent related to the provision of price information. The feasibility of regularly providing physicians with price information is discussed and reviewed in light of other approaches that have been developed to modify physician behavior in ordering diagnositc tests.