We investigated the effect of intratracheally instilled coal fly ash (FA) and copper smelter dust (CU) on the lung integrity and on the ex vivo release of tumor necrosis factor alpha (TNF-α) by alveolar phagocytes. Croups of female NMRI mice received a single intratra cheal administration of different particles normalized for the arsenic content (20 μg/kg body weight, i.e., 600 ng arsenic/mouse) and the particle load (100 mg/kg body weight, i.e., 3 mg/mouse). Mice received tungsten carbide (WC) alone (100 mg/kg), FA alone (100 mg/kg, i.e., 20 μg arsenic/kg), CU mixed with WC (CU, 13.6 mg/kg, i.e., 20 μg arsenic/kg; WC, 86.4 mg/kg) and Ca3(AsO4)2mixed with WC (20 μg arsenic/kg; WC, 100 mg/kg). Animals were sacrificed at 1, 6, or 30 d posttreatment and analyzed by bronchoalveolar lavage for total protein (TP) content, inflammatory cell number and type, and TNF-α production. Additional mice were studied to evaluate particle retention by measuring total arsenic retention in the lung at appropriate times. Instillation of WC induced a mild and transient (d 1) inflammatory reaction characterized by an increase of TP and an influx of polymorphonuclear leukocytes in the alveolar compartment. Compared to WC, Ca3(AsO4)2produced a significant increase of TP content in BALF. CU particles caused a severe but transient inflammatory reaction, while a persisting alveolitis (30 d) was observed after treatment with FA. Compared to control saline, a marked inhi bition of TNF-α release was observed in response to LPS in all groups at d 1. Cytokine production was upregulated in WC- and Ca3(AsO4)2-treated animals after 6 and 30 d, respectively. However, a 90% inhibition of TNF-α production was still observed at d 30 after administration of CU and FA. Although arsenic was cleared from the lung tissue 6 d after Ca3(As04)2administration, a significant fraction persisted (10-15% of the arsenic administered) in the lung of CU- and FA-treated mice at d 30. We hypothetize that sup pression of TNF-α production is dependent upon the slow elimination of the particles and their metal content from the lung.