The research described in this paper is part of a project aimed at improving energy costs and the indoor environment of atrium buildings. Tracer gas techniques were used to assess the ventilation performance in terms of air distribution and contaminant migration patterns and to measure the air infiltration rate of a three-storey atrium. This atrium serves as an entrance to a large office-laboratory complex. The results indicate that even though the HVAC systems of the test atrium are connected to the building complex, tracer gas techniques were successfully used to determine the air distribution and contaminant migration patterns, and the air infiltration rate. A detailed description of the methods used and the test results are presented.