Cell-free DNA that originates from cell death, circulates in peripheral blood. There are indications that the infarcted myocardium contributes to an increase of cell-free DNA levels. Our aims were to quantify levels of cell-free DNA in patients with acute myocardial infarction (AMI) and examine their correlation with myocardial markers and with postinfarction (PI) clinical course. Thirteen patients (age 57 +/- 16 year) admitted with AMI and who underwent thrombolysis with reteplase within 6 h from the onset of chest pain were studied. PB samples were collected on admission and for 5 consecutive days. Creatine kinase (CK) and troponin I (TnI) were measured on admission and every 8 h for 3 consecutive days. Clinical events were recorded throughout the hospitalization period. Cell-free DNA levels were also measured in 30 healthy controls. Log-transformed mean (+/-SE) of maximum free DNA values in patients higher than controls (6873 +/- 357 g.e./mL verses 4112 +/- 234 g.e./mL, P < 0.0001). Log-transformed maximum values of CK and TnI were correlated with log-transformed free DNA values of first (r = 0.62, P = 0.02/r = 0.68, P = 0.01) and second (r = 0.57, P = 0.04/r = 0.72, P = 0.0053) PI day. Nine patients (group A) had an uncomplicated PI clinical course and four patients (group B) had recorded events (three with angina and one death). Free DNA levels on the second PI day were higher in group B than group A (1298.0 +/- 796.0 g.e./mL verses 244.6 +/- 257.7 g.e./mL, P = 0.003). In conclusion, free DNA levels are significantly higher in patients with AMI than in controls and may play a role in the prognosis of these patients.