Background/Aims: Interferon-alpha is used widely to treat viral hepatitis. Interferon-gamma modulates a system attacking infected cells and also has an anti-fibrotic effect. A treatment with interferon-alpha and -gamma has undergone trials in eliminating hepatitis C virus. We investigated effects of cotreatment in a liver fibrosis model to explore anti-fibrotic effects. Methods: Rats were assigned to groups including normal controls (NC), CCl(4) controls, rat interferon-alpha treatment, rat interferon-gamma treatment, and cotreatment. All groups except normal controls received CCl(4) orally for 8 weeks. At the beginning of the third week of exposure, 6 weeks of treatment were initiated according to interferon group. Digitally analyzed immunohistochemistry, biochemical assays, and Northern analysis were performed. Results: Pixels (x10(5)) per field containing immunoreactive type III collagen (fibrotic density) in CCl(4) controls, interferon-alpha, interferon-gamma, and cotreatment groups respectively were [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]. Liver hydroxyproline content correlated with fibrotic density, and was significantly low in the cotreatment group. Plasma hyaluronate and transaminase were significantly low in cotreatment and interferon-alpha groups. Northern blotting showed lowest mRNA expression for type I collagen, desmin, transforming growth factor (TGF)-beta1, and matrix metalloproteinase-2 mRNA in the cotreatment group; tissue inhibitor of metalloproteinase-1 and -2 mRNAs were significantly low in the interferon-gamma group. Conclusions: Cotreatment can suppress collagen and transforming growth factor-beta1 and has an overall anti-fibrotic effect without exacerbating inflammation.