Recently, it was demonstrated that bradykinin (BK) enhances intracarotid delivery of herpes simplex virus type I (HSV) vectors to rat brain tumors, and that gene transfer takes place predominantly in the tumor periphery. The aim of the present study was to apply these findings to the treatment of experimental rat brain tumors. The HSV mutant, hrR3, which is disrupted in the ribonucleotide reductase gene, was injected intra-arterially with titers of 1 x 10(8), 1 X 10(9), and 1 x 10(10) plaque-forming units (pfu) both with and without BK into Fischer 344 rats with intracerebral, syngeneic 9L tumors. Starting on day 3 after vector administration, animals were treated by intraperitoneal injection of 60 mg/kg/day ganciclovir (GCV) or placebo. 1 x 10(10) pfu hrR3 in combination with BK and GCV treatment was able to eradicate tumors in 80% of the animals; 1 x 10(9) pfu cured 40% of the rats, and 1 x 10(8) pfu achieved an extension of survival time but no tumor cures. Control groups had 100% mortality within 30 days after injection of tumor cells, with the exception of the group with injection of 1 x 10(10) pfu of virus and GCV treatment, which had one long-term survivor. No apparent complications of this novel type of brain tumor gene therapy were encountered. In conclusion, intra-arterial injection of attenuated HSV vectors with blood-tumor barrier modification and subsequent systemic GCV application appears to be a promising approach for the treatment of malignant brain tumors.