Compared with control group, the mRNA expressions of MMP-2 and MMP-9 in the lung tissue of ALI group were increased at 6 hours (MMP-2 mRNA: 1.88±0.09 vs. 1.00±0.10, MMP-9 mRNA: 3.15±0.47 vs. 1.00±0.17, both P<0.01); they were down-regulated in UFH group (MMP-2 mRNA: 1.26±0.14 vs. 1.88±0.09, P<0.01; MMP-9 mRNA: 2.06±0.68 vs. 3.15±0.47, P<0.05), but still above the control group (both P<0.05).