A plan has been developed for assessing the air quality of non-industrial buildings. It consists of ten tasks. Tasks 1 and 2 are designed to obtain the background information on the building itself, its surroundings and occupants. Task 3 provides an opportunity for the project team to review theresults and to determine if an in-depth study is necessary. Tasks 4, 5 and 6assess the performance of the building's HVAC systems and identify the contaminants present. Task 7 calls for another review to select the contaminants which are to be monitored continuously and to decide if medical and other specialists are required to assist in the investigation. Task 8 specifies a series of tests to establish the basis for remedial measures and to estimate the additional ventilation air required to cope with anticipated changes in the contamination loads. Task 9 is intended to obtain additional information, and to check the air change rates and contamination levels after the remedial measures have been implemented. Task 10 is the preparation of the final report. The length of the investigation is about a year. The plan is being checked in an eight storey library-office building. Thus far, no major problems have been experienced.