The accumulation of toxic or otherwise harmful trace gases in a spacecraft cabin is a very serious concern in terms of the health and safety of the crew. Although methods exist for controlling the evolution of such contaminants, techniques for monitoring the success of these methods, on board and in near- real-time, are still under development. One such technique, based on the use of FTIR interferometry, is being developed in Europe. A prototype instrument has been assembled, making extensive use of 'off-the-shelf' hardware and software, and tested for its ability to detect and quantify--within a maximum period of 1 minute and in the presence of water vapour and carbon dioxide 21 of the most frequently detected contaminants on past Shuttle and Spacelab flights. Results have confirmed that such contaminants can be detected and measured with an acceptable degree of precision.