This paper describes the current state of technology for evaluating gas removal filters designed for cabin air filtration.Many automobile manufacturers are aware of the importance of a filtration system to improve cabin air quality. This can be seen by the increasing number of vehicles being produced with such systems in Europe and Japan. The air in the interior of a vehicle contains particulate and gaseous pollutants such as dust, pollen, soot, tobacco smoke, hydrocarbons, oxides of carbon, sulfur and nitrogen (e.g., CO, SO2, NO2), and ozone. To effectively reduce the level of particulate matter entering the vehicle's ventilation system, filters using electrostatically charged media have become the industry standard due to their combination of high particle capture efficiencies, low pressure drop and long life. In combination with these, filters for effectively removing gaseous pollutants are also being developed.The factors affecting the performance of gas removal filters are complex and to properly evaluate their performance a practical, yet technically sound test method must be used. A significant effort has been put forth to understand these factors and a useful test method for measuring filter performance has been developed.