A single-cylinder DI Diesel engine was fumigated with ethanol and methanol in amounts up to 55% of the total fuel energy. The primary objectives of this work were to determine the effects of aqueous alcohol fumigation on engine thermal efficiency, combustion intensity and gaseous exhaust emissions. Assessment of changes in the biological activity of raw particulate and its soluble organic fraction were also made using the Ames Salmonella typhimurium test.Alcohol fumigation improved thermal efficiency slightly at moderate and heavy loads, but increased ignition delay at all operating conditions. Carbon monoxide emission generally increased with alcohol fumigation and showed no dependence on alcohol type or quality. Oxides of nitrogen emission showed a strong dependence on alcohol quality; relative NOX levels decreased with increasing water content of the fumigant. Particulate mass loading rates were lower for ethanol-fueled conditions. However, the biological activity of both the raw particulate and its soluble organic fraction was enhanced by ethanol fumigation at most operating conditions.