Tp53 is frequently mutated or inactivated in glioblastomas. Due to the impairment of p53 activity, glioblastomas show a high degree of radioresistance. In an attempt to convert the radioresistant phenotype to a more radiosensitive one, we evaluated the efficacy of the combination of Adp53 gene transfer and X-ray irradiation. The combination of Adp53, at low multiplicity in order to mimic the low in vivo efficiency of virus-mediated gene delivery, with X-ray irradiation resulted in a marked decrease of glioblastoms cell survival. Interestingly, Adp53 was able to induce low dose (<2Gy) hypersensitivity. The data suggest the possibility for the development of new therapeutic strategies.