Thrombolytic therapy has been shown to be very effective in the acute phase of myocardial infarction and the benefits are greater if the treatment is initiated as soon as possible. In France, early treatment in the prehospital phase is possible through the SAMU, an emergency ambulance and care unit organisation. Between December 1987 and November 1988, 80 patients (73 men and 7 women) with an average age of 55 +/- 9 years were treated by rt-PA (100 mg i.v. in 90 minutes) for acute myocardial infarction within three and a half hours of the onset of symptoms. The average delay between the onset of pain and the administration of rt-PA was 126 +/- 43 minutes, which represents an estimated average time gain of 55 minutes compared with thrombolysis started after hospital admission. No haemorrhagic or allergic complications occurred during hospital transfer and there was no mortality. There were, however, two diagnostic errors. Thrombolysis was estimated to be effective on clinical, electrocardiographic and enzymatic criteria in 60 p. 100 of cases. Thirty early coronary angiographies (within 48 hours) showed that 83 p. 100 of the arteries thought to be responsible for the infarct were patent. Haemorrhage was a rare complication during the hospital phase and had a favourable outcome. Hospital mortality was 6 per cent. The low morbidity and the reliability of diagnosis indicate that prehospital thrombolysis is feasible in the acute phase of myocardial infarction.