The effects of a prolyl 4-hydroxylase inhibitor (HOE 077) on tissue inhibitor of metalloproteinase-1 (TIMP-1) and procollagen type I were examined in rat liver fibrosis. HOE 077 (200 ppm) prevented fibrosis by inhibiting the expression of liver type I procollagen and TIMP-1 mRNAs, with liver hydroxyroline content correlated with the reduction in activated stellate cells. HOE 077 prevents fibrosis by inhibiting proline hydroxylation and stellate cell activation, resulting in reduced expression of procollagen and TIMP-1 mRNAs.