The prehospital time interval in 103 patients with acute myocardial infarction was investigated. Twenty patients were admitted with cardiac arrest. In the remaining patients the average total delay was found to be 3.3 hours and the patient delay 1.5 hours. The total delay was significantly prolonged in patients who were admitted during working hours, patients who were unaffected on admission, patients transported for long distances, patients who had been visited by their doctors prior to admission and patients who contacted their own doctors. The authors find that attempts should be made to reduce these delays by means of information both to the public and to doctors.