This report describes exhaust-emission data from 10 diesel engines: six 4-cycle, direct-injection, naturally aspirated engines; two 4- cycle, direct-injection, turbocharged engines; one 4-cycle, precombustion-chamber, turbocharged engine; and one 2-cycle, direct- injection engine. These engines were tested over a 3-year period (1968-70). Lowest emissions were obtained with a precombustion- chamber engine. Emissions from the 2-cycle, direct-injection engine fell within the range of emission rates for the 4-cycle, naturally aspirated, direct-injection engines. Excluding the precombustion- chamber engine and excepting one of the 4-cycle, naturally aspirated engines, carbon monoxide emission rates were about the same for all engines tested. Test data on smoke, odor, and emissions of hydrocarbons, oxides of nitrogen, carbon monoxide, and aldehydes are given. Work done under an agreement with the Environmental Protection Agency.