Based on the registration of all the 7,157 patients admitted during a 21-month period to the emergency ward of a single hospital in an urban area with chest pain or other symptoms suggestive of acute myocardial infarction, we studied eligibility for intravenous thrombolysis in suspected acute myocardial infarction. We have limited the present analysis to those 1,715 patients with a strong suspicion of myocardial infarction, and for these patients, we have calculated the percentages eligible for thrombolysis when various electrocardiographic and delay time criteria are applied, but we have not considered contraindications to thrombolysis. We have also calculated the proportions of all infarctions in this group that would thereby receive the treatment, and the proportions of patients treated that would develop a confirmed infarction. Using the criteria ST elevation on the initial electrocardiogram and arrival in hospital within 6 hours from onset of symptoms, 18% of patients would have been given early intravenous thrombolysis, 37% of confirmed infarctions would have been treated, and 91% of all treated patients would have developed a confirmed infarction; with a delay time criterion of 12 hours, these percentages would have been 209%, 41%, and 91%, respectively; with a criterion of 24 hours, they would have been 22%, 45%, and 90%, respectively. By not considering the initial electrocardiogram and applying only the criterion of delay time, these percentages would have been 70%, 72%, and 45%, respectively, for a delay time of 6 hours; 83%, 84%, and 45%, respectively, for a delay time of 12 hours; and 91%, 92%, and 44%, respectively, for a delay time of 24 hours. We have also calculated these percentages for two further electrocardiographic criteria, namely, electrocardiogram showing acute ischemia and any form of pathology. We conclude that the percentage of patients with a strong suspicion of myocardial infarction eligible for intravenous thrombolysis varies considerably depending on the electrocardiographic and delay time criteria used. If the delay time is limited to 6 hours and the electrocardiogram is required to show ST elevation, then 37% of patients developing myocardial infarction would receive thrombolytic treatment.