Out-of-hospital emergency care was designed around the concept of a system of interrelated events that combine to offer a patient the best care possible outside the hospital. However, in contrast to the actual operations of emergency medical service (EMS) systems, research has not typically used systems-based models as the method for evaluation. In this discussion we outline the weaknesses of component-based research models in EMS evaluation and attempt to provide a "systems-analysis" framework that can be used for future research. Incorporation of this multidiscipline approach into EMS research is essential if there is to be any hope of finding answers to many of the important questions that remain in the arena of out-of-hospital health care.