Procalcitonin (PCT) is implicated as an inflammatory marker in early atherosclerosis. In order to investigate the clinical consequences of increased PCT levels in acute coronary syndrome (ACS), 77 patients (29 with non-ST-elevation myocardial infarction [MI], 34 with ST-elevation MI and 14 with unstable angina pectoris) were included and followed up for 6 months. The PCT levels were determined at initial presentation and within 48 h of admission. Five patients died during hospitalization and their PCT levels within 48 h of admission were significantly higher than survivors (n = 72) (0.588 +/- 0.56 versus 0.399 +/- 1.33 ng/ml, respectively). The PCT levels within 48 h post-admission in the nine patients who died within 6 months were also significantly higher compared with the survivors (0.451 +/- 0.44 versus 0.406 +/- 1.37 ng/ml, respectively). It is concluded that higher PCT levels within 48 h post-admission may reflect an inflammatory state that is associated with increased early and 6-month mortality.