BACKGROUND The aim of the present study was to investigate differences of matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 in the peripheral blood of patients admitted with acute coronary syndrome (ACS), in correlation with the widely accepted markers of inflammatory activity, C-reactive protein, fibrinogen, and white blood cell number. METHODS 315 patients with ACS (165 unstable angina pectoris/non-ST-elevation myocardial infarction, 150 ST-elevation myocardial infarction), 111 stable angina (SA) patients, and 296 control subjects were enrolled in the study. All biochemical analyses were carried out using a Hitachi 912 analyzer (Roche). Matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) levels were determined in citrate plasma by ELISA methods. White blood cells (WBC) and fibrinogen were also determined. RESULTS The plasma concentrations of matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1, C-reactive protein, fibrinogen, and white blood cells in patients with acute coronary syndrome were significantly elevated compared to the control group (p < 0.001). MMP-9/TIMP-1 ratio was significantly higher in SA and ACS patients (p < 0.001) than controls. Strong positive associations were observed between MMP-9 and TIMP-1 (r = 0.213, p < 0.01), MMP-9 and CRP (r = 0.103, p < 0.01), MMP-9 and fibrinogen (r = 0.299, p < 0.01), MMP-9 and WBC (r = 0.135, p < 0.01), TIMP-1 and CRP (r = 0.219, p < 0.01), TIMP-1 and Fibrinogen (r = 0.226, p < 0.01), TIMP-1 and WBC (r = 0.094, p < 0.1), CRP and fibrinogen (r = 0.158, p < 0.01), CRP and WBC (r = 0.156, p < 0.01, and finally between fibrinogen and WBC (r = 0.234, p < 0.01) in the patients with ACS. CONCLUSIONS In conclusion, our observations suggest that ACS shows an increase in both remodeling and inflammation markers. In addition, the strong relationship with MMP-9 and inflammatory mediators such as CRP, fibrinogen, and WBC in ACS patients suggests that MMP-9 might be an additional marker and/or consequence of inflammatory components in ACS.