In order to define the extent of gas and particulate emissions from automotive brakes (and clutches), a combination separation and storage collection system was devised. Unique emissions collectors for both disc and drum brakes and for a clutch were conceived, designed, and built as the main embodiment of this instrumentation. The hardware was installed on a vehicle which was then driven through various test cycles to determine the extent and type of brake emissions generated at low- and high-operating temperatures. Typical driving conditions such as the Detroit Traffic Test as well as more abusive driving conditions such as fade tests were included.Typical original equipment and aftermarket friction materials for both disc and drum brakes were used in the tests. Brake relines were made to simulate typical consumer-type practices. The brake emissions generated were removed from the various collectors and mass balances were performed. The particulates were processed and analyzed by a combination of optical and electron microscopy to ascertain the asbestos content and the asbestos particle size distribution in the wear debris. Comparisons of emissions from new and used friction materials, from disc and drum brakes, and from original equipment and aftermarket materials were made. Finally, an estimate was made of the total emission of asbestos by all of the vehicles in the country. On the average more than 99.7% of the asbestos is converted. The contribution to the atmosphere is 5060 lb or 3.2% of the total asbestos emission.