An investigation was undertaken to determine if gasoline additives could effect a reduction in exhaust HC emissions. Of the multitude of compounds studied, two were found to reduce the increase in HC emissions associated with the accumulation of lead-derived combustion chamber deposits by approximately 50%. A practical combination of these compounds was evaluated in a fleet test which confirmed laboratory engine results. Studies were also conducted in laboratory engines and fleet vehicles to determine the effect of fuel lead level upon this additive's effectiveness and the activity of the additive upon established lead-derived combustion chamber deposits. Results obtained from these programs indicated that the additive would function with fuel lead levels from 1/2-3 g/gal, but that it was not capable of modifying established deposits. A rationale for the observed effect is presented.