Dr. Jack Harkema and colleagues at Michigan State University conducted a 2-year study with rats to evaluate the short-term effects of inhaling concentrated ambient particles derived from the air in an area of Detroit, Michigan that has a high incidence of childhood asthma. The investigators used two animal models, BN rats that were sensitized with ovalbumin to induce some features of asthma, and F344 rats pretreated with endotoxin to have some features of mild bronchitis. Animals were exposed for 10 hours/day for 1 day or for 4 or 5 consecutive days. The investigators assessed the effects the particles had on airway inflammation and hypersecretion of the mucus. In addition, the investigators explored the toxicity of the metal elements in the particles.