The influence of fuel composition on exhaust emissions from four 1982 model light-duty diesel vehicles was studied on the FTP cycle and at two steady-state conditions, but only the FTP results are presented and discussed in this paper. Nine test fuels were blended specifically for the program, with intentional variation in aromatic content, 90% boiling point, and 10% boiling point. Limited data were also acquired with injection timing at advanced and retarded settings, in addition to the main body of data taken with the engines adjusted to recommended timing. A comparatively small effort was also made to evaluate a tenth fuel consisting of a blend of two of the original nine fuels. Of the fuel characteristics varied intentionally, aromatic content generally had the greatest effect on most emissions of major interest (hydrocarbons, oxides of nitrogen, particulate, soluble organic fraction, polynuclear aromatic hydrocarbons, and mutagenicity of extract by Ames bioassay). Effects of 90% boiling point were strongest on fuel economy, due to its association with fuel density. Effects of 10% boiling point on emissions were comparatively weak and mixed.The vehicles responded quite differently to fuel property changes, primarily in magnitude of effects, although sometimes also in direction of effects. Changes to injection timing also caused measurable changes in fuel effects for a number of cases.