The effectiveness of six commercial water-displacing corrosion preventive formulations (WDCP's) in inhibiting corrosion of two aluminium alloys used in aircraft construction has been investigated. Two solutions, 0.1 molar sodium chloride and 0.1 molar sodium chloride-0,18 molar aluminium chloride, were chosen to simulate aircraft service environments in the laboratory tests. Testing was done by treating specimens with WDCP's prior to exposure to the corrosive media and also by immersing specimens in the test media and then adding WDCP's to these solutions. Evaluation was by weight loss measurements and subsequent microscopic examination. In some of the tests, a novel method of estimating weight loss (during the course of a test) by analysis of small samples os solution was used. All six WDCP's tested were found to inhibit corrosion of the aluminium alloys significantly under the test conditions.