Governmental regulation of emergency medical services and transportation differs from state to state. In Arizona, the Department of Health Services (ADHS) regulates the provision of ambulance service through a "certificate-of-necessity" (CON) process. Paramedic rescue services provided by municipalities are not, by statute, mandated to comply with these ADHS regulations. We review the way in which criteria for the determination of ambulance need were adopted by this state agency and the effects of their application in Tucson, Arizona. Approximately one million dollars and 5,500 unnecessary "code 3" (lights and siren activated) emergency vehicle trips were mandated by the ADHS need criteria, over a twelve-month period. We conclude that non-scientifically-derived regulatory criteria may conflict with prudent medical control of prehospital emergency medical services (EMS).