While support for the development of clinical guidelines is widespread, there is little agreement about how they should be used. Because cost control is the force behind the medical effectiveness movement, the payers' preference, to link clinical guidelines to reimbursement, will likely prevail. We examine the utilization review programs of Medicare Part B carriers and the carriers' attempts to use clinical guidelines to determine medical necessity for the purpose of payment. We find that because the utilization review programs are driven by concerns about cost control, the carriers' actual review process relies on aggregate utilization and spending targets that have little to do with clinical guidelines. The carriers' medical review rhetoric--using the terms medically unnecessary and fraud and abuse as synonyms--also highlights their focus on cost control and the lack of concern about why services are used inappropriately.