We found that a concentration of 1 μM, i.e. within its therapeutic range [22], dexamethasone significantly inhibited the bystander effect on C6, LN18 and U87 glioma cells co-cultured with small proportions (5–20 %) of C6-TK, LN18-TK and U87-TK cells. This evidence concerns the gene TKT and glioma.