Objective: Impression tray adhesives are delivered in glass bottles with a fixed brush attached inside the cap. If the adhesive is applied on a worn denture or on a tried-in and therefore contaminated impression tray with the brush, microorganism can be transferred into the bottle. Using the adhesive with the same brush at another patient may cause cross-contamination. This study tested tray adhesives for the risk of cross contamination by evaluating their antibacterial properties. Method: Bacterial solutions at 107 cfu/ml made of commercially available in-vitro-test strains and bacterial strains isolated from human saliva were plated on Columbia-agar-plates. Tray adhesive was applied to the centre of the agar-plates and incubated for 48h. The expansion of the biological inhibition assays were measured microscopically. One alginate-adhesive (Fix/Dentsply), a silicone-adhesive (Universal/Heraeus) and a polyether-adhesive (3MESPE) were tested. Results: 21 bacterial strains were selected in the saliva samples of 20 test patients. The overgrowth of the patient strains was 1 % (± 0.3) for the alginate-, 12 % (± 5) for the silicone- and 31 % (± 9) for the polyether-adhesive. The in-vitro-test strains showed an overgrowth of 1 % ± (0.3) for the alginate-, 7 % (± 1) for the silicone- and 7 % (± 2) for the polyether-adhesive. Therefore the adhesives had no antibacterial properties. Conclusion: In-vitro-testing did not show antibacterial properties of tray adhesives. Consequently, there is at least a risk of cross-contamination if a brush is used twice and replaced into the adhesive. It is suggested not to use the brushes, but cast the adhesive into a Dappen-dish and apply the adhesive with a cotton pellet. Keywords: Dental materials, Impression materials, Infection, Microbiology and Oral hygiene