INTRODUCTION The objective of the project was to investigate the nature and identity of molecular species encountered in a diesel exhaust reproducibly available from the same engine operated under the same conditions with the same fuel. Emphasis was placed on those species that by sensory assay were rated as significant odor contributors. The isolation and identification of the odor-relevant components in diesel exhaust required the application of effective sampling and analysis techniques suitable for handling complex mixtures of organic substances in the presence of a large excess of water vapor. The direct sampling from a nitrogen-diluted exhaust progressed to solid-adsorbent-phase collectors which completely extracted all possibly odor relevant organic vapors from a diluted exhaust flow. Separation of components in the collected sample was achieved by high resolution gas chromatography. Support-coated open tubular columns with Apiezon L and Carbowax 20M stationary phases were used for the initial analyses of exhaust samples in a single column chromatograph which provided for odor analysis in parallel with flame ionization detection. Further sample resolution and partial component characterization through polarity dispersion were achieved with a twocolumn chromatograph. The dual-column system comprised two high resolution columns of different polarity@ Carbowax 20M and Apiezon L@ connected in series@ with the option of selecting the portions of the first column effluent to be injected onto the second column. Odor analysis was performed on the effluent from each column. With the two-column chromatograph@ sufficient isolation of the odor-relevant species from the bulk of non-odorous components was obtained to allow the selected trapping of odorous compounds for mass spectrometric identification with a specially designed interfacing unit.