Background and methods: Gene therapy may offer a new tool for the treatment of renal cell carcinoma ( RCC ). We have tested a combination of cytotoxic and antiangiogenic gene therapy for wild -type orthotopic human RCC xenografts in nude mice using intratumoral adenovirus -mediated herpes simplex virus thymidine kinase ( HSV -tk ) and endostatin ( ES ) gene therapy. In vivo magnetic resonance imaging, morphometry, immunocytochemistry, and survival were used to evaluate the treatment effect. Adenovirus -mediated marker gene transfers ( GFP ) were used as controls. Results: In vivo transduction efficiency, measured using GFP gene transfer, was 27 ± 7%. The combination gene therapy with HSV -tk and ES adenoviruses resulted in a significant antitumor effect ( P < .01 ) compared to single HSV -tk ( n.s. ) or ES ( n.s. ). In the survival study, all tumors with single gene therapy using HSV -tk, ES, and marker gene adenoviruses showed progression in magnetic resonance imaging. In contrast, the majority of the tumors in the combination treatment group remained dormant or were eradicated ( 57% ). Survival of these mice equaled healthy nude mice, and was significantly prolonged ( P < .0001 ) compared to HSV -tk ( P < .028 ) and ES ( n.s. ) groups. Conclusions: It is concluded that the inhibition of angiogenesis using ES gene transfer together with the cytotoxic HSV -tk gene therapy results in a significantly improved treatment effect in RCC compared to the single gene treatments.