The report gives results of a study of a commonly used commercially available ozone generator, undertaken to determine its impact on indoor ozone levels. Experiments were conducted in a typical mechanically ventilated office and in a test house. The generated ozone and the in-room ozone concentrations were measured. The results showed that, when the unit was operated at the manufacturer's recommended setting, it generated little if any ozone. The indoor concentrations in the case were not significantly above natural background. When operated at the maximum setting, the generator produced large amounts of ozone: over 100 ppb in well ventilated spaces, and nearly 1 ppm in poorly ventilated spaces. When the ozone generator was turned off, ozone levels quickly returned to background. No measurements were made to determine the effect of the device on other aspects of indoor air quality, such as the elimination of volatile organic compounds.