Objective To study the serum and cerebrospinal fluid(CSF) concentrations of Methotrexate(MTX) and the toxicity effect between two different dosages of high-dose MTX (3 g/m 2,5 g/m 2) in the treatment of acute lymphocytic leukemia(ALL) in children.Methods Ninty-eight dosages of HD-MTX(including 3 g/m 2 and 5 g/m 2) were given to 43 cases of ALL children. The serum and CSF concentrations of MTX and the incidence of adverse reaction of the drug between 2 groups of high-dose MTX(3 g/m 2,5 g/m 2) were compared.R...