A sample of 20 in-use light-duty diesel vehicles were extensively and repeatedly tested for two years. Gaseous and particulate emissions were measured for the FTP, HFET, CFDS, NYCC, 50 mph cruise, and idle driving cycles. Vehicles were tested with both as-received and control fuel and lubricating oil. Particulate extracts were obtained by Soxhlet extraction with dichloromethane, and the extracts assayed for mutagenic activity by the Ames Salmonella typhimurium/microsome method with TA98(-) tester strain. Particulate, extract, residue, hydrocarbons, carbon monoxide, nitrogen oxides, % extractible, fuel economy and Ames activity are discussed as they relate to driving cycles and mileage accumulation. Driving cycles were found to affect emissions more strongly and consistently than does mileage accumulation. Cycle and mileage effects were observed in some cases for Ames activity but were not well defined.