This paper describes the use of carbon-14 radiolabeled succinimides and succinate esters to investigate the role of ashless dispersants in controlling deposit formation in gasoline engines. Analysis of used oils, varnish deposits, and insolubles from several gasoline engine tests showed that: 1. Ashless dispersants were not significantly broken down chemically in service. 2. Dispersants played an active role in the processes leading to deposits and were evenly distributed in varnish throughout the engine. 3. Insolubles in the oil were agglomerations of small, primary particles of about 300-400 diameter. 4. A major portion of the dispersant in used oils was bound up with polar organic and inorganic species and was unable to assist in dispersing particles.The implication of these findings on the development of new additives and crankcase oil formulations is discussed.