Dr Günter Oberdörster and colleagues at the University of Rochester School of Medicine and Dentistry hypothesized that inhaled ultrafine particles induce an inflammatory response in the airways of mice and rats and that animals with preexisting airway inflammatory conditions may be particularly vulnerable. The investigators focused on inhaled carbon and platinum particles because these elements are constituents of particles found in urban atmospheres. They also evaluated the effects of Teflon fumes containing ultrafine Teflon particles which have been shown to induce a potent inflammatory response leading to severe physiologic effects in rats. The investigators tested a small number of young and old mice and rats that were healthy or had preexisting airway inflammatory conditions. Pulmonary inflammation was evaluated by measurement of cellular and biochemical parameters in bronchoalveolar lavage fluid, focusing on increases in the percentage of neutrophils and production of reactive oxygen species, which appeared to be the most sensitive indicators of a response.