Aim: Numerous investigations have found active metallomatrix proteinase 8 (aMMP-8) to be a relevant inflammatory marker for early stages of periodontal tissue destruction. The first chairside aMMP-8 test just recently entered the market. It was the aim of this prospective, monocenter case-control study to compare the diagnostic accuracy of this chairside test (PerioMarker® aMMP-8 Schnelltest von Chlorhexamed®) with the conventional laboratory method (ELISA). Methods: For this study, 35 periodontally healthy participants, 60 patients who had gingivitis, and 35 periodontitis patients were recruited. In order to differentiate between the groups, the periodontal screening index was applied. Primary variable was the aMMP-8 chairside test result. Secondary variables were aMMP-8 ELISA test results, plaque index, gingivitis index, bleeding on probing, periodontal pocket depths, clinical attachment level. Parameters were recorded at baseline and after therapy. Healthy participants did not receive any therapy; parameter recording took place at baseline and after four weeks. Gingivitis patients received a dental prophylaxis, periodontitis patients received a deep scaling. Both patient groups were recalled 12 weeks after baseline. Positive and negative agreement [%] between test and control methods was calculated as measure of diagnostic accuracy. The agreement between aMMP-8 concentrations and clinical parameters before and after therapy was assessed by means of contingency tables. Results: Positive agreement between both aMMP-8 methods was found in 75.8% (95%-CI 57.7 - 88.9%). Negative agreement was found in 92.8% (95%-CI: 85.7% - 97.0%). In total, the agreement of test results was kappa=0.692 before therapy and kappa=0.693 after therapy. The percentage of positive test results increased strongly from healthy participants to periodontitis patients. Conclusion: The chairside aMMP-8 test is as exact as ELISA to detect increased MMP-8 activity in patients who have gingivitis and periodontitis. Negative test results indicate healthy periodontal conditions. Keywords: biomarker, aMMP8, parodontitis, chairside test