In the present study, we genotyped 2 polymorphisms in MTHFR (rs1801133 and rs1801131) and 2 more polymorphisms in SLCO1B1 (rs4149056 and rs11045879) in Japanese ALL/NHL patients treated with HD-MTX and examined the relationship between genotypes and prognosis/adverse events. Here, MTHFR is linked to acute lymphoblastic leukemia.