A multiple tracer gas method for following air movement in buildings has been developed and demonstrated at the Polytechnic of Central London. This paper describes the method andshows how it is being used to investigate: 1. the whole house infiltration rate of three experimental solar houses at Peterborough, U.K., 2. the transfer of warm air from passively heated conservatiories to the living spaces, and 3. transfer between the ground and first floors. The method allows up to four perfluorocarbon tracer gases to be released simultaneously in different parts of a building. The tracers are liquids at room temperature, and the release mechanism uses flash heaters operated remotely. An automatic sampling system, employing the principle of gas adsorption by a solid adsorbent is used to take spot samples of air containing the tracer gases. Sampling tubes packed with adsorbent, are arranged in groups of up to ten, at as many as five different sampling points. Samples are taken simultaneously at each sample point and in a timed sequence. The tracer gases are quantitatively retrieved from the sampling tubes using an automatic thermal desorber, and analysed using a gas chromatograph fitted with a packed column and a flame ionisation detector. The analysis is controlled and data is collected by a low cost microcomputer. The project was funded by the U.K. Science and Engineering Research Council and grateful acknowledgement is made to Chris Martin for assistance with the micro-interfaces and the mathematical analysis of gas concentration data.