Background. Matrix metalloproteinases (MMPs), especially MMP-8, play an important role in tissue destruction and remodeling in course of periodontal diseases. Some information suggests that the measurement of MMP-8 concentration in gingival crevicular fluid (GCF) may provide a useful and objective tool for periodontal diagnostics and periodontium assessment. Objectives. Assessment of the MMP-8 levels in GCF in patients with mild, moderate and advanced chronic periodontitis as well as in control group and searching for the correlation between the levels of MMP-8 in GCF and periodontal clinical status. Material and Methods. The study included 92 patients (45 females and 47 males). In each patient the clinical attachment loss (CAL), gingival index (GI), approximal plaque index (API), and pocket depth (PD) were recorded. The control group consisted of 16 patients with healthy periodontium. Patients with chronic periodontitis were divided into three groups according to CAL: patients with mild periodontitis (CAL from 1 to 2 mm, 23 patients), patients with moderate periodontitis (CAL from 3 to 4 mm, 29 patients), and patients with advanced periodontitis (CAL equal to or greater than 5 mm, 24 patients). GCF samples were collected with sterile Periopaper strips that were inserted into the gingival crevice until mild resistance was felt and then left in place for 30 s. MMP-8 levels in GCF were measured by enzyme-linked immunosorbent assay (ELISA). Results. We found that level of MMP-8 increased with the severity of periodontitis. In patients with advanced chronic periodontitis level of MMP-8 in GCF was on average 18.5 +/- 6.4 ng/ml and was sevenfold higher than in patients with healthy periodontium. Moreover, in patients with advanced chronic periodontitis level of MMP-8 in GCF was higher than in patients with mild (mean concentration of MMP-8 was 5.8 +/- 6.3 ng/ml) and moderate (mean concentration of MMP-8 was 16.0 +/- 8.6 ng/ml) periodontitis. Statistical analysis revealed strong correlation between the level of MMP-8 in GCF and PD (r = 0.72), GI index (r = 0.61) and clinical attachment loss (r = 0.60). Conclusions. Our results indicated that the assessment of MMP-8 concentration in GCF might be an objective marker of periodontitis severity