The paper describes several experiments to evaluate the impact of indoor air pollutant sources on indoor air quality (IAQ). Measured pollutant concentrations are compared with concentrations predicted by an IAQ model. The measured concentrations are in excellent agreement with the predictions. The model predictions and the experimental data demonstrate the importance of sinks in determining long term IAQ. An objective of EPA's IAQ program is to provide guidance on the impact of indoor pollutant sources on IAQ. A computer model, EXPOSURE, was developed to assist in the effort. EXPOSURE calculates pollutant concentration as a function of time for each room in a building. EXPOSURE includes the effects of sources, sinks, room-to-room air movement, and air exchange with the outdoors.