Our previous studies showed that genetic variability in the key folate pathway enzymes, 5,10-methylenetetrahydrofolate dehydrogenase 1 (MTHFD1), 5,10-methylenetetrahydrofolate reductase (MTHFR), and thymidylate synthase (TYMS), might influence MTX pharmacokinetics and treatment outcome in children with ALL.3,4 Therefore, the aim of the present study was to assess the influence of polymorphisms in these genes on HDMTX-related toxicity in children with NHL treated according to Berlin-Frankfurt-Münster (BFM) protocols. This evidence concerns the gene TYMS and acute lymphoblastic leukemia.