The aim of this study is to assess the performance of the mechanical ventilation system and air quality in an office building. The perfluorocarbon tracer (PFT) technique was used to measure air flow in an air handling unit and to estimate flow rates supplied to the office. In order to validate the PFT technique as a viable means of measuring air flow in the mechanical ventilation system, the PFT measurements were compared with measurements made using a pitot-static tube. Air exchange range, ventilation effectiveness and age of air were examined. The concentrations of carbon dioxide (C02), carbon monoxide (CO), formaldehyde (HCHO) and dust particles were monitored. In addition, a questionnaire was completed by the staff in order to provide a subjective assessment of indoor air quality.