lnadequate ventilation is often cited as the cause of unhealthy air quality within office buildings, whilst excessive ventilation is similarly assumed to be the cause of discomfort and energy waste. However, the reality is that very little data is available to assess the significance of these problems on any large scale. The perfuorocarbon tracer (PFT) technique offers the potential for overcoming the problems of applying conventional tracer gas techniques to large or multi-roomed buildings.