In chronic hepatitis C, the main goal of antiviral therapies is to block viral replication and to slow down the development of fibrosis. In this study, a decrease in matrix metalloprotease-9 (MMP-9) but not of MMP-2 and the tissue inhibitors of MMP (TIMP-1 and TMP-2) was observed in the plasma of chronic hepatitis C patients at the end of the follow-up period after ribavirin plus interferon-alpha2b (PEG-IFN-alpha2b) treatment in sustained virologic responders but not in nonresponders. Consistently, similar results are observed by immunofluorescence and real-time PCR in tissue specimens collected before and after therapy from the same patients in whom both Kupffer cells and hepatocytes express MMP-9. In conclusion, our results show that MMP-9 decreases in responder patients both in the serum and in the liver after therapy. Further studies are needed to investigate this new possible therapeutic activity of PEG-IFN-alpha2b.