A major concern in emergency medical services (EMS) planning has been the need to minimize ambulance response time, only one of several delays in reaching definitive care. Other important delays include patient delay in seeking medical care and dispatch delay. In this study, the importance of response time in light of other delays is discussed, and response time as one determinant of patient survival is analyzed, using Seattle's EMS system as a case study. The major conclusion is that paramedic response times influence short-term patient survival.