To asses O6-MGMT promoter methylation in the mentioned glioma studies, several different methods have been employed, as was recently pointed out by van den Bent et al(12), who stressed the point that the CpG island in that part of the gene actually contains almost 100 individual CpG sites and that the used methods only give information on the methylation status of a few of these sites. Here, MGMT is linked to central nervous system cancer.