Background: Difficulties in diagnosis of inflammatory bowel disease (IBD) motivate the search for new diagnostic tools, including laboratory tests. The aim of this study was to evaluate concentrations of the neutrophil (NEU) proteins leukocyte elastase (HLE-alpha 1AT), lactoferrin and calprotectin as potential biomarkers used in the diagnosis and assessment of clinical activity of Crohn's disease (CD) and ulcerative colitis (UC). Material/Methods: The study included 27 patients with CD, 33 patients with UC and 20 healthy controls. Plasma concentrations of calprotectin, lactoferrin and HLE-alpha 1AT were measured using ELISA. Results: In patients with CD higher concentrations of HLE-alpha 1AT (64.3 +/- 43.1 vs. 30.1 +/- 7.7 ng/l, P<0.001), calprotectin (151.6 +/- 97.8 vs. 69.9 +/- 22.1 ng/l, P<0.001) and lactoferrin (243.2 +/- 102.0 vs. 129.7 +/- 32.7 ng/l, P<0.001) than in the control group were found. In patients with UC higher plasma concentrations of HLE-alpha 1AT (62.0 +/- 30.9 vs. 30.1 +/- 7.7 ng/l, P<0.001), calprotectin (149.6 +/- 72.3 vs. 69.9 +/- 22.1 ng/l, P<0.001) and lactoferrin (242.6 +/- 107.5 vs 129.7 +/- 32.7 ng/l, P<0.001) than in the control group were found. HLE-alpha 1AT/NEU and lactoferrin/NEU ratios in patients with UC were significantly higher compared with patients with CD. Calprotectin (P=0.010) and lactoferrin (P=0.023) levels were higher in patients with the active compared with inactive phase of CD. Conclusions: The diagnostic characteristics of plasma granulocyte protein concentrations indicate the usefulness of these tests in the diagnosis of IBD. Higher HLE-alpha 1AT and lactoferrin/NEU ratios in patients with UC than with CD may suggest the usefulness of these ratios in differential diagnostics. Plasma calprotectin and lactoferrin levels may be useful in CD activity assessment.