Particulate and gaseous emissions from two light-duty diesel automobiles were examined over six operating cycles. Particulate characterizations included mass emission rate, soluble organic content, and trace element content determinations. The particulate matter was sampled using both a total filtration system having 20 X 20 inch filters and a conventional probe arrangement employing 47 mm filters. Bioassay of selected diesel particulate extract was carried out using the Ames test procedure. Gaseous characterization included real-time analysis of regulated exhaust emissions. A special operating schedule was developed for each test car using the real time system to modally determine the effect of acceleration rate on regulated gaseous emissions.