For a patient to derive maximal benefit from intravenous thrombolytic therapy for acute myocardial infarction, early treatment is essential. As part of the Thrombolysis in Myocardial Infarction II trial, this study investigated the time delays that preceded treatment of 236 consecutive patients with intravenous tissue-plasminogen activator (TPA) during acute myocardial infarction. The average (+/- SD) time from the onset of symptoms to treatment with TPA was 153 +/- 54 minutes. After arrival in the emergency department, patients waited an average of 19.9 +/- 17.8 minutes for the initial electrocardiogram. Following the diagnosis of acute myocardial infarction by electrocardiogram, an additional 70 +/- 40 minutes elapsed before thrombolytic therapy began. The interval between the initial electrocardiogram and initiation of treatment with TPA was less when the drug was first administered in the emergency department (46.8 +/- 23.4 minutes) rather than after transfer to the coronary care unit (82.1 +/- 34.7 minutes). In-hospital delays at the two academic and two private hospitals accounted for more than half of the total time from the onset of symptoms to initiation of thrombolytic therapy. We conclude that significant in-hospital delays are likely to occur before a patient receives thrombolytic therapy for acute myocardial infarction. Various factors conspire to create these delays, but a well-organized team approach to treatment will help to minimize delays in the implementation of this new form of therapy.