Both experimental and clinical studies suggest that the prehospital administration of aspirin may be beneficial in patients with unstable angina and acute myocardial infarction. Experimental studies indicate that within 1 hour of aspirin administration, serum levels peak and significant inhibition of platelet aggregation occurs. Clinical studies demonstrate that early treatment with aspirin reduces mortality and reinfarction rates in patients with unstable angina and acute myocardial infarction. However, these same studies also indicate that prolonged delays often occur before in-hospital therapy with aspirin is initiated. Since the potential benefits are great and the risks and costs are low, physicians should encourage the prehospital administration of aspirin in patients with symptoms suggestive of unstable angina or acute myocardial infarction.