A tale of two diesels.

Two different samples of diesel exhaust particles (DEP) have been used by toxicologists interested primarily in cancer/genotoxicity or noncancer--such as pulmonary inflammation and asthma exacerbation--health end points. These are, respectively, a standard reference material, SRM 2975, from a heavy-duty diesel engine, and a sample collected by researchers at the Japanese National Institute for Environmental Studies from an automobile diesel engine. In this issue of Environmental Health Perspectives companion papers appear, by David DeMarini and co-workers and by Pramila Singh and co-workers, characterizing these samples and contrasting their Salmonella mutagenicity and pulmonary toxicity in mice. This commentary is a plea from an atmospheric chemist for more cooperation among toxicologists, analytical chemists, atmospheric chemists, and automotive and combustion engineers to provide a comprehensive assessment of health risks to humans exposed to contemporary diesel emissions and for greater quantities and more diverse types of DEP and ambient samples (i.e., SRMs) that can be shared and exhaustively characterized. This needs to be a continuing process as diesel engines, fuels, and exhaust components evolve in response to control regulations.