This report describes a study by Drs. Yu and Yoon to mathematically predict the lung burden in rats and humans of diesel exhaust particles (DEP) from automobile emissions. Building on a previously constructed model describing DEP deposition, the present work focused on clearance and retention of DEPs deposited in the lung. The transport rates of each component of DEPs were derived using experimental data and mathematical approximations. The complete model was first developed for rats and then extrapolated to humans of different age groups.