The paper gives results of a characterization of ozone emissions from air cleaners equipped with ozone generators and sensor and feedback control circuitry. Ozone emission rates of several consumer appliances, marketed as indoor air treatment or air purification systems, were determined in a well-characterized 30-cubic meter environmental chamber. Additional tests were conducted in a research test house to determine the effects of appliances on research house ozone concentrations and to evaluate the performance of an ozone generator feedback control system. Ozone emission rates determined in the chamber studies ranged from 0.5 to > 150 mg/hr for one appliance at 50% relative humidity (RH). Ozone emission rates increased as RH decreased for all models tested. Nitrogen dioxide generation rates ranged from 0.06 to 0.16 times the ozone emission rate and varied among models of different manufacturers.