Background: Circulating cardiac troponin I (cTnI) is a sensitive biochemical marker for detection of myocardial cell damage and has been shown to be related to adverse short term prognosis in patients (pts) with acute coronary syndrome (ACS). We investigated prospectively the value of rapid bedside cTnI testing in n = 773 pts with acute chest pain but without ST-elevation in the electrocardiogram (ECG) in the emergency room for short-term outcome.Methods: Samples were taken on admission (5.2 +/- 4.0, range 1.0-12.0 hrs after onset of chest pain) and after a 4 hrs interval. Test results were related to 30-days outcome with respect to death or acute myocardial infarction (AMI).Results: By the time of admission n = 109 pts had positive cTnI > 0.1 ng/ml, after a 4 hrs interval 62 additional pts were cTnI positive. Within a 30-day follow-up n = 34 cardiac events occurred, which was preceded by elevated cTnI in the initial specimen in n = 19 pts (56%) and in n = 13 pts more (94%) 4 hrs after admission (>6 hrs after onset of pain).Conclusions: In pts with ACS presenting with acute chest pain but without ST-elevation admission cTnI measurements allow reliable risk stratification. Due to low sensitivity a single result on admission is insufficient, a second measurement 6 hrs after onset of chest pain is mandatory for adequate risk assessment.