Hepatocellular carcinoma (HCC) is regarded as a suitable target for antiangiogenic strategies. However, antiangiogenic agents aimed at single targets can be neutralized by upregulation of other proangiogenic factors. Therefore, combined approaches addressing at least two angiogenic targets should be more effective. Employing an appropriate rat hepatoma model, we examined the effects of sFlt-1 (soluble vascular endothelial growth factor [VEGF] receptor 1 as an indirect inhibitor of angiogenesis) and endostatin (a direct inhibitor of angiogenesis) in both single-agent as well as combined approaches under in vitro and in vivo conditions. Similar to human HCC, rat Morris hepatoma (MH) cells secreted high levels of VEGF, but no endogenous sFlt-1. Parental MH or MHES(r) cells, stably expressing rat endostatin, were adenovirally transduced either with AdsFlt-1 (encoding sFlt-1) or control vector Adnull (containing no transgene), followed by subcutaneous inoculation into syngeneic ACI rats. Compared with MH/Adnull cells, expressing no antiangiogenic factors at all, tumor weights were reduced fourfold in the MHES(r)/Adnull group, 19-fold in the MH/AdsFlt-1-group, and 77-fold in the MHES(r)/AdsFlt-1 combination therapy group. Analysis of variance did not show a significant interaction between the effects of the two factors ES(r) and sFlt-1; their effects multiplied. In conclusion, combined expression of sFlt-1 and endostatin effectively suppresses HCC growth under in vivo conditions.