"The Neely Conference: Developing Research Criteria to Define Medical Necessity in EMS" convened emergency medical services (EMS) physicians, researchers, administrators, providers, and federal agency representatives to begin the development of a set of uniform triage criteria and outcome measures that could be used to study and evaluate medical necessity among EMS patients. These standardized criteria might be used in research studies examining EMS dispatch and response (e.g., dispatch triage protocols, alternative response configurations), and EMS treatment and transport (e.g., field triage protocols, alternative care destinations). The conference process included review and analysis of the literature, expert judgment, and consensus building. There was general agreement on the following: 1. Any dispatch triage or field triage system that is developed must be designed to offer patients alternatives to EMS, not to refuse care to patients. 2. It is theoretically possible to develop a set of clinical criteria for need. Some groups of patients will clearly need a traditional EMS response and other groups will not, but this has yet to be defined. 3. In addition to clinical criteria, certain social and other nonclinical criteria such as pain or potential abuse may be used to justify a response. 4. Communication barriers, patient age, special needs, and other conditions complicate patient assessment but should not exclude patients from consideration for alternate triage or transport. 5. These research questions are important, and standard sets of outcome measures are needed so that different studies and innovative programs can be compared.