BAL analysis of pulmonary injury and inflammation. Mice were exposed by inhalation exposure to air (vehicle) or MWCNTs (5 mg/m3) for 12 days. BAL LDH and BAL PMNs studies were conducted at 1, 14, 28, 84, 168 and 336 days post-exposure. Cytotoxicity was assessed by BAL fluid LDH activities and pulmonary inflammation by BAL polymorphonuclear leukocytes. BAL fluid LDH activities (upper panel) and BAL PMNs (lower panel) were significantly elevated above respective clean-air controls from 1 to 168 days post-exposure (Mean ± S.E., N = 6-8). An asterisk indicates air-exposed controls were significantly lower (p < 0.05) in comparison to the corresponding MWCNT-exposed group. Highly significant decreases in LDH (P < 0.0001) and BAL PMNs (P < 0.002) with post-exposure time were determined. BAL protein was also measured and followed the same pattern as LDH (data not shown).