In endemic fluorosis areas in China associated with coal burning, indoor airborne fluoride pollution is severe. To determine the effects of fluoride aerosols on pulmonary antibacterial defense mechanisms and lung damage, mice were exposed to various concentrations of fluoride aerosol (2, 5, or 10 mg/m3) or filtered air (control) for 14 d, 4 h/d in an inhalation chamber. Bactericidal activity against Staphylococcus aureus in the lung and the number and profile of free pulmonary cells, protein content, and lactate dehydrogenase (LDH) activity in bronchoalveolar lavage (BAL) fluid were assessed. Urinary fluoride concentration, an indicator of fluoride exposure, increased in proportion to fluoride aerosol concentration in the chamber. Wet lung weight was significantly higher on d 14 in mice exposed to 10 mg/m3 than in controls. Pulmonary bactericidal activity against S. aureus was concentration-dependently suppressed at 5 and 10 mg/m3 fluoride. The number of alveolar macrophages (AMs) in the BAL fluid of the mice not bacterially challenged decreased significantly at 10 mg/m3 fluoride. The number of polymorphonuclear leukocytes and lymphocytes increased significantly at 10 mg/m3 fluoride exposure. The concentration of total protein (TP) and albumin in BAL supernatant increased significantly at 5 and 10 mg/m3 fluoride exposure, and LDH activity rose markedly at the higher fluoride concentration. Data indicate that fluoride inhalation produces pulmonary cellular alterations that are associated with a diminished ability to cope with infectious bacteria.