This paper describes tracer gas measurements at the National Museum of Fine Arts in Stockholm. The building was erected 1850-1860 and the architect was Friedrich August Stüler. He created several museums of Fine Arts, among them Neues Museum in Berlin. The museum building in Stockholm has a volume of almost 90 000 m3 and the number of registered objects of art is well over 600 000. The collection includes one of the world’s most prestigious collections of drawings and graphical prints. In this case study the aim was to determine the infiltration through the main entrance and stairwell, through windows and outside walls. The measurement technique used was the Homogeneous Emission Technique added with a 2-zone set up, by using two different tracer gases. Several interesting results were obtained. One result was that more airtight entrance doors would decrease the infiltration into the main stairwell with 40 %. Another result of interest was that the very dry outdoor air was mixed with the indoor air quickly, and that the

mechanical ventilation system with filters and humidifying units has to be upgraded to compensate for the outdoor air infiltration.