Thrombolytic therapy for acute myocardial infarction (AMI) is now routinely given in the emergency department and is being considered for pre-hospital care. Its effectiveness is dependent on how early it can be given after the onset of AMI. Maximal benefit, however, is not realized in many patients due to delay in seeking care. The effect of a public media education campaign (message) to shorten patient delay and increase use of emergency medical services (EMS) was evaluated prospectively in King County, Washington. We interviewed 401 patients admitted with possible AMI in the premessage period (4.5 months) and 489 in the postmessage period (4.5 months). The two groups were comparable in all factors except for discharge diagnosis of AMI (premessage, 34%; postmessage, 25%; P less than .01) and history of myocardial infarction or angina (premessage, 52%; postmessage, 43%; P less than .01). The proportion of patients who heard new information on AMI increased significantly in the postmessage period (premessage, 53%; postmessage, 74%; P less than .0001). The campaign, however, did not significantly shorten patient delay in seeking care (median delay: premessage, 2.6 hours; postmessage, 2.3 hours) or alter the distribution of patients in the less-than-two-hour, two-to-four-hour, and more-than-four-hour intervals. The rate of EMS use also was not significantly changed (premessage, 42%; postmessage, 44%). We conclude that a short-duration education campaign may increase AMI knowledge but does not seem to significantly alter patient behavior.