AIM: To test the hypothesis that enhancement of the activity of heme oxygenase can interfere with processes of fibrogenesis associated with recurrent liver injury, we investigated the therapeutic potential of over-expression of heme oxygense-1 in a CCl(4)-induced micronodular cirrhosis model. METHODS: Recombinant adeno-associated viruses carrying rat HO-1 or GFP gene were generated. 1x 10(12) vg of adeno-associated viruses were administered through portal injection at the time of the induction of liver fibrosis. RESULTS: Conditioning the rat liver with over-expression of HO-1 by rAAV/HO-1 significantly increased the HO enzymatic activities in a stable manner. The development of micronodular cirrhosis was significantly inhibited in rAAV/HO-1-transduced animals as compared to controls. Portal hypertension was markedly diminished in rAAV/HO-1-transduced animals as compared to controls, whereas there are no significant changes in systolic blood pressure. This finding was accompanied with improved liver biochemistry, less infiltrating macrophages and less activated hepatic stellate cells (HSCs) in rAAV/HO-1-transduced livers. CONCLUSION: Enhancement of HO activity in the livers suppresses the development of cirrhosis.