BACKGROUND AND OBJECTIVES: In the early phase of acute chest pain, the diagnosis of acute coronary syndrome (ACS) is often difficult to achieve in an emergency department (ED) due to the non-diagnostic ECG and cardiac markers. Ischemia modified albumin (IMA) has recently been shown to be a sensitive early biochemical marker of ischemia. The aim of this study was to evaluate the diagnostic value of IMA for the patients with suspected ACS and who have normal ECG/cardiac markers. SUBJECTS AND METHODS: We enrolled 142 consecutive patients who presented to the ED due to suspected ACS, and they had a normal EKG and troponin-I/CK-MB within 5 hours after the onset of their chest pain. The diagnosis of ACS was based upon the clinical findings, the results of serial ECG/troponin and the coronary angiography. The ideal cutoff value of IMA for ACS was calculated by the receiver operator characteristic (ROC) curve analysis. RESULTS: The ACS was diagnosed in 80/142 (56%). The ROC curve area for the IMA test was 0.77 (CI; 0.70-0.85, p<0.01). At a cutoff value of 98.5 U/mL, the sensitivity, specificity and negative predictive values for ACS were 73%, 75% and 75%, respectively. At a cutoff value of 85 U/mL, the sensitivity and specificity and negative predictive values for ACS were 92%, 35% and 95%, respectively. CONCLUSION: IMA might be a useful diagnostic marker of ACS for those patients with normal ECG/cardiac markers and who present within 5 hours after the onset of chest pain.