Background: Thrombolytic therapy has been shown to reduce mortality in select patients with acute myocardial infarction (AMI). The determinants of eligibility for therapy are changing as more information about the safety and efficacy of thrombolytic therapy is obtained. In the United States, there is some concern that thrombolytic therapy is underutilized, particularly in women and older patients. The purpose of this investigation is to examine change in the use of thrombolytic therapy in a single community from the years 1988 to 1992. Particular attention was paid to women and older patients. Methods: From January 1988 through December 1992, 9154 patients who developed AMI were admitted to coronary care units in 19 hospitals in the metropolitan Seattle area. The hospital records of each consecutive patient were reviewed, and key information was entered into the Myocardial Infarction Triage and Intervention database. Patients who developed AMI after hospital admission for another medical condition were excluded, as were the small numbers of patients with AMI complicated by cardiac arrest and resuscitation prior to hospital admission. This population-based study contains first admissions for AMI during the 5 year period of the registry. Results: The use of thrombolytic therapy in all patients increased from 18% to 24% (p <.0001) during the 5 year period; women (10-16%) and patients 75 years and older (3-10%) had proportionately greater increases in utilization. Despite widespread awareness of its importance, the median time from symptom onset to hospital arrival did not change during the 5 years, although there was a slight decrease in the time from hospital arrival to treatment with thrombolytic therapy. Conclusions: The change in use of thrombolytic therapy indicates that age and gender are less often used as exclusions for receiving thrombolytic therapy. It is possible that exclusionary criteria are being modified, with the result that this important treatment is being received by more people. The finding that there was no change in the time from acute symptom onset to hospital arrival requires intensive study. In particular, more needs to be known about patient decisionmaking, and innovative community interventions to reduce delay times must be evaluated.