Organic oils, like those used in mouthrinses can, due to their hydrophobe behavior, contribute to the dilution or eluation of substances from periodontal pockets, if they are used for subgingival irrigation.Neutrophil elastase is a proteolytic enzyme known for its destructive potential also of periodontal tissues. Its activity in gingival crevicular fluid (GCF) is a suitable marker to monitor periodontal and gingival inflammation. The aim of the present study was to determine the effect of two different solutions for pocket irrigations on the elastolytic activity (EA) in GCF. In a prospective, randomized double-blind study 20 patients with severe chronic periodontitis were included based on radiographic and clinical parameters. They had at least 3 teeth in the upper jaw with one site probing pocket depth (PD more than 5 mm). After a period of initial plaque control (14 days) an examination phase of 90 days followed. The clinical parameters assessed were a modified plaque index (PLI), 4 sites/tooth, as well as probing pocket depth, bleeding on probing (BOP) and attachment level at 6 sites/tooth. On the days -14, 0, 15, 28, and 90 the patients underwent a complete clinical examination. All clinical measurements performed were using a Florida Probe® and reference acrylic stents. During the experimental phase, prior to clinical examination two samples of GCF were taken at 3 test teeth using Periopaper® on the days 0, 1, 3, 15, 28, and 90. After sample collection and clinical probings all sites PD more than 5 mm were rinsed. The liquids used were 1 ml of oil in the test group respectively 0,9% NaCl in the control group. The sample volumes were analyzed with Periotron 8000® and the elastolytic activity was measured with the Fluostar®. In the test group a decline of the median - EA from 2839 µU/µl (day 0) to 1892 (day 1) and 1137 µU/µl (day 3) could be observed. At the end of the study the median -EA had reached its initial level again. The control group did not show any comparable findings.The results show that a subgingival irrigation with soy bean oil in this frequency decreases EA of inflamed periodontal pockets considerably. Keywords: soy bean oil, pocket irrigation, elastolytic activity, gingival crevicular fluid, periodontal therapy, Florida Probe, Periotron 8000, Periopaper, Fluostar