A light-duty automotive Diesel engine was fumigated with ethanol in amounts up to 50% of the total fuel energy. The main purpose of this study was to determine the effect of ethanol fumigation on engine performance at various operating conditions. Engine fuel efficiency, emissions, smoke, and the occurrence of severe knock were the parameters used to evaluate performance. Raw particulate and its soluble organic extract were screened for biological activity using the Ames Salmonella typhimurium assay.Results are given for a test matrix made up of twelve steady-state operating conditions, For all conditions except the 1/4 rack (light load) condition, modest thermal efficiency gains were noted upon fumigation. However, engine roughness or the occurrence of severe knock limited the maximum amount of ethanol that could be fumigated. Brake specific NOX concentrations were found to decrease for all conditions tested. Based on the limited particulate data analyzed, it appears as though ethanol fumigation, while lowering the mass of particulate emitted, does enhance the biological activity of that particulate.