The Assessment of the Safety and Efficacy of a New Thrombolytic 3 (ASSENT 3 PLUS) Plus trial (n=1639) was an international trial of pre-hospital fibrinolysis with tenecteplase randomly assigned to enoxaparin or unfractionated heparin, involving 106 sites in 12 countries. Given the potential impact of process of care delivery in various healthcare systems, we undertook a comprehensive validated survey of population demographics, geographical factors, emergency medical services, methods of electrocardiogram interpretation and pre-hospital fibrinolysis administration. The potential study population was 42.4 x 10(6) with 70% urban. The land areas of individual emergency medical services sites varied from 6 to 20000/km(2). Three emergency medical services personnel (range 2-5) attended each ambulance with the highest level of training, consisting of a physician (65%), registered nurse (20%) or paramedic. Before the initiation of the study, 72% of sites administered pre-hospital fibrinolysis (range 1-20 years). Electrocardiograms were interpreted on the scene in 60% and transmitted for physician's interpretation in the remainder; 41% of patients (679/1639) were enrolled at sites without a physician at the scene. The ASSENT 3 Plus trial incorporated a wide variation in population density, emergency medical services resources, and physician's interpretation of ECG and administering pre-hospital fibrinolysis. Understanding this diversity will help in evaluating the general applicability and feasibility of pre-hospital fibrinolysis in various health systems, as well as the pre-hospital care of ST elevation myocardial infarction patients regardless of reperfusion strategies.