We have previously demonstrated that intratracheal instillation (IT) with diesel exhaust particles (DEP) exacerbates myocardial ischemia/reperfusion-induced arrhythmia in rats. Since activated neutrophils play a pivotal role in ischemia/reperfusion arrhythmia, in the present study we investigated the effects of DEP on peripheral neutrophil count and on the oxyradical production (ORP) of neutrophils in rats. We also determined the production of cytokines for better understanding of the relationship between pulmonary inflammation and neutrophil function. Instillation with 5 mg DEP elevated circulatory neutrophil counts (CNC) at 12 and 24 h post-instillation to levels approximately 2.1- and 2.3-fold those in the vehicle-treated animals, respectively. On the other hand, 1-mg DEP caused an approximately 0.4-fold increase in CNC at 6 h. 12-O-Tetradecanoylphorbol 13-acetate-induced ORP in the isolated neutrophil was enhanced at 12 and 24 h after instillation with 5 mg DEP. Cytokine-induced neutrophil chemoattractant-1 (CINC-1), tumor necrosis factor-alpha (TNFalpha) and macrophage inflammatory protein-2 (MIP-2) levels were increased in the bronchoalveolar lavage fluid (BALF) collected from animals that received 5 mg DEP. In serum, a marked elevation of CINC-1 and a slight elevation of MIP-2 were also observed, while TNFalpha was not detected. Granulocyte-macrophage colony-stimulating factor (GM-CSF) was detected in neither BALF nor serum for 24 h after the instillation. These results suggest that IT instillation of DEP enhances systemic oxidative stress by increasing neutrophil count and ORP in the acute period.