MGMT status is now regarded as a strong predictive factor of response to standard treatment of newly diagnosed glioblastomas involving temozolomide (TMZ) and radiotherapy. MGMT promoter methylation is also a prognostic factor - independent of treatment - in anaplastic gliomas. The predictive function can be explained by the role of the DNA repair enzyme MGMT, which antagonizes the effects of alkylating agents such as TMZ. MGMT promoter methylation could also reflect a particular molecular phenotype with its own specific prognostic significance. Since MGMT status determination is becoming a crucial biological marker in new clinical glioma trials, and is beginning to be used in day-to-day clinical practice, there is currently a strong need to determine the best technique for MGMT analysis. A French multicenter study has been set up for this purpose.