Inflammatory processes play a role in the onset of acute cardiovascular events associated with activation of the coagulation system whereas the fibrinolytic system may prevent local thrombus formation. We compared 25 patients with premature coronary artery disease (CAD) (first ST-elevation myocardial infarction, < 55 years old) with 25 sex-matched patients older than 55 years at their first myocardial infarction. Six months after the acute event, patients with late onset of CAD showed a significantly higher increase of tissue-type plasminogen activator activity during venous occlusion compared with patients with premature CAD (P < 0.005). Prothrombin fragment 1+2 was higher in patients with late-onset CAD (P < 0.05), whereas the inflammatory markers C-reactive protein and soluble intercellular cell adhesion molecule-1 were not different in both groups. A multivariate analysis including cardiovascular risk factors showed that the tissue-type plasminogen activator response to venous occlusion was independently associated with patient age at onset of first ST-elevation myocardial infarction. Although in our series high age was associated with a prothrombotic state, a high fibrinolytic capacity might have some beneficial effect and contribute to a delayed onset of adverse cardiovascular events in these patients.