Steady-state mRNA levels and immunoreactive protein for manganese-containing superoxide dismutase (MnSOD) were assayed in rat lungs after subchronic inhalation of the fibrogenic silicon dioxide, cristobalite, or preparations of titanium dioxide (TiO2) of different inflammatory and fibrogenic potential. Total and differential cell counts recoverable by bronchoalveolar lavage (BAL) were also measured to ascertain whether induction of certain antioxidant enzymes (AOE) correlated with inflammatory responses. Inhalation of cristobalite and ultra-fine TiO2, a particle causing pulmonary inflammation and fibrosis, caused dramatic increases in MnSOD mRNA levels in rat lung which correlated with increases in MnSOD immunoreactive protein. Increases in gene expression of other AOE [catalase, glutathione peroxidase (GPX), copper-zinc containing superoxide dismutase (CuZnSOD)] were less striking and did not correlate precisely with inflammatory potential of minerals. Inflammatory changes in BAL correlated directly with steady-state MnSOD mRNA levels in lung. Inhalation of TiO2-F, a noninflammatory, nonfibrogenic mineral, failed to induce MnSOD or mRNAs for other AOE. Our data suggest that particles causing inflammation and pulmonary fibrosis increase expression of AOE in lung, most notably MnSOD. Thus, elevations of MnSOD mRNA levels in lung or BAL may be predictive of lung disease.