The paper compares design specifications for three large (room-sized) environmental chambers. The chambers, while intended for similar purposes (for use in characterizing sources of indoor air pollution), have been designed and constructed by Australian, Canadian, and U.S. government research organizations to different specifications. The first phase of the interlaboratory comparison study consists of a comparison of the design specifications and construction of the three systems. The three systems show many characteristics in common. Each has a sealed room-sized polishd stainless steel chamber, with an air supply that is filtered, dehumidified, passed through activated carbon to remove volatile organic compounds, and conditioned to an appropriate temperature and relative humidity. There is built-in capability to sample for indoor air emissions, and sense temperature and relative humidity. Construction materials and components were selected for their ease of disassembly and re-assembly for cleaning.