O6-méthylguanine méthyltransférase (MGMT) is the main repair gene after DNA lesion induced by Temozolomide in combination with radiation therapy of Glioblastoma (GBM) in Stupp.R et al published regimen. In preclinical models, it has been demonstrated that MGMT methylation (which is silencing the DNA repair process) is achievable by folic acid. About half of the patients with operated GBM have an un-methylated MGMT gene status and therefore a poorer prognosis. A phase-1 dose escalation study is proposed with pharmacologic doses of folinic acid in combination with temozolomide and radiotherapy of operated GBM.