The paper gives results of a study of a single-story office building, relating air cleaner efficiency to indoor air quality. Predicting the improvement in indoor air quality due to in-duct air cleaners is an important aspect of ventilation system design. The effects of percentage of outdoor makeup air, filtration, and occupancy on mass concentrations and particle size distributions were recorded. Particle size dependent filtration efficiencies for a variety of air cleaners, including those in use in the test building, were determined. A multizone indoor air quality simulator, IAQPC, was used to simulate the conditions in the building. The building's layout, ventilation system design, and filtration efficiency data were entered. A comparison of simulator to experimental results showed good agreement. To determine the effect of various mitigation procedures, IAQPC and the building's data set were used to model the air concentrations for several types of filters and an electronic air cleaner. In addition, the effect of changing sources was examined.