Diesel engines are a source of suspended ambient particulate matter, and some concerns have been raised about the health effects from the inhalation of these particles. Nitrated polycyclic aromatics adsorbed on these particles have been shown to have the potential to cause mutations in living cells. Particulate matter collected on teflon-coated glass fiber filters produces results that may be open to question because of the possible generation of artifactual nitrated aromatics during the filtration process.An experiment using a constant-volume combustion bomb was used with four oxidants (air, nitrogen-free oxidant (29% O2 21% Ar 50% CO2), 50% O2/50% N2, and O2 (99.95% pure)), to address the concern over artifactual generation of nitrated-PAH on the filtration medium. Soot samples were collected both in situ on a cooled plug and on teflon-coated glass fiber filters in the exhaust line. Chemical comparisons of the collected samples were accomplished using chromatographic procedures. Biological comparison of the extracted material from the soot was accomplished using the Ames Salmonella test.The biological activity from the filter and plug samples for each oxidant showed no significant differences for three of the oxidants. This was consistent with the gas-chromatographic results in which little difference was found between the filter and plug samples for each oxidant.