In order to test the performance of the interior systems of a proposed passively daylighted office building, a full-scale mock-up of a portion of that building was constructed. Using appropriate instrumentation, tests were performed to determine the quality of lighting, acoustics, and air distri-bution under various anticipated operating conditions. Based on the results of the initial tests, certain architectural modifications were made before proceeding to a final series of tests. The mock-up demonstrated that a radically new energy-efficient building design can be tested and performance problems corrected before actual construction. In addition, the mock-up was used to develop performance specifications--used later in the bid process--for products that will comprise the interior systems of the building.