Experiments were performed to determine the effects of temperature and lead content of the fuel on the weight and size distribution of particulates emitted from a spark ignition engine. The measurements were made using three different, specially constructed sampling systems which utilized filters and an Andersen Sampler for particle collection, and allowed sampling directly from the exhaust stream. The performance of these sampling systems was evaluated, and the conditions necessary for obtaining a representative sample of the exhaust stream were established. Measuring both leaded and unleaded fuels, the total weight of particles emitted using leaded fuel was approximately six times higher than with unleaded fuel. Particulate deposition on the inside of the exhaust system was also evaluated.