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To identify the size and components related to toxicity of ambient particles, we used a trichotomous impactor to collect 17 sets of particles in three size ranges--submicrometer (diameters < 1 microm; PM1.0, fine (diameters between 1 and 2.5 microm; PM1.0-2.5, and coarse (diameters between 2.5 and 10 microm; PM2.5-10--at stations monitoring background, urban, traffic, and industrial air in Taiwan. Elemental contents, carbon contents, soluble ions, and endotoxin content of particles were determined by X-ray fluorescence spectrometry, thermal analysis, ion chromatography, and the Limulus amebocyte lysate assay, respectively. Human bronchial epithelial BEAS-2B cells were exposed to particle extracts at 100 micro g/mL for 8 hr, and interleukin-8 (IL-8) concentrations in the medium and lipid peroxidation products were measured. Particle-induced tumor necrosis factor-alpha (TNF-alpha) production by mouse macrophage RAW 264.7 cells was also measured. PM1.0 stimulation resulted in significantly higher IL-8 production and lipid peroxidation than PM2.5-10, whereas the responses elicited by PM1.0-2.5 were not significantly higher than blank filters. Untreated and polymyxin B-pretreated PM1.0 also stimulated more TNF-alpha production by RAW 264.7 cells than PM2.5-10 and PM1.0-2.5. Cytokine production was significantly associated with metal contents of PM1.0: IL-8 correlated with Cr and Mn, and TNF-alpha correlated with Fe and Cr. Lipid peroxidation in BEAS-2B cells correlated with elemental and organic carbon contents. Our study found that size and composition of ambient particles were both important factors in inducing cytokine production and lipid peroxidation.