Acute exposure to hyperoxia results in well-described pathophysiologic responses in the lungs, beginning with subtle, subcellular changes and ending with severe pulmonary inflammation and edema. The biologic events that underlie or accompany this injury are not well understood. Our previous studies in rabbits have shown that hyperoxia induces large increases in the mRNAs encoding metallothionein (MT) and the tissue inhibitor of metalloproteinases (TIMP-I). Here we report studies of hyperoxic lung injury in two strains of mouse that differ in their relative resistance to O2 toxicity. O2-sensitive (C57BL/6J) mice and O2-resistant (C3H/HeJ) mice were exposed to 100% O2 for up to 96 h. Lung mRNAs were assayed by primer extension and slot blot hybridization. By 72 h of hyperoxia, the sensitive strain showed large increases in MT-I, MT-II, and TIMP-I mRNAs. The resistant strain showed similar changes but with a 24-h delay. In situ hybridization demonstrated that hyperoxic lung injury was accompanied by obvious increases in TIMP-I and MT transcripts in cells surrounding arteries and large airways, where many inflammatory cells were localized. With prolonged exposure, hybridization to MT transcripts had spread throughout lung parenchyma. The two strains showed the same patterns of in situ hybridization for TIMP-I and MT transcripts but, as with the whole lung homogenates, followed a different time course. Corresponding increases in MT protein were shown to occur, using a cadmium binding assay and by immunohistochemistry. The strong spatial correlation between the presence of localized inflammation and increased TIMP-I and MT expression further supports the importance of TIMP-I and MT in acute lung injury.