Matrix metalloproteinases (MMP) have been thought to be involved in stroke pathogenesis. MMP-9 contributes to tissue destruction. Our aim was to analyze the MMP-9 levels in blood within 24 hours of acute ischemic stroke onset to observe the role of MMP-9 in the pathogenesis of atherothrombotic stroke. In this study we investigated prospectively MMP-9 levels in serum from 106 patients (42 men and 64 women, mean age 71.52 +/- 6.32 years) with acute ischemic stroke in the middle cerebral artery area in the first 24 hours from the onset (mean duration 7.8 +/- 4.5 hours) as compared to 112 controls (48 men and 64 women, mean age 70.36 +/- 6.8 years). Serum samples were collected under sterile conditions and stored in aliquots at -70 degrees C until assay. Serum MMP-9 levels were determined by enzyme-linked immunosorbent assay (ELISA) in blood samples obtained on admission. Statistical analysis was performed by Mann-Whitney and Log-Likeliwood Ratio tests. All values reported are expressed as mean (x) +/- SD. Mean serum MMP-9 concentrations were higher in group with ischemic stroke 172 +/- 32.4 ng/mL, range 139.6-204.4 ng/mL vs. controls 57 +/- 9.6 ng/mL, range 47.4-66.6 ng/mL (95% CI, 3.17 to 14.18; p < 0.014). In conclusion, MMP-9 activity is associated with early acute ischemic stroke. The high levels of MMP-9 in acute ischemic stroke document the involvement of this enzyme in the regulation of inflammation in stroke.