Dose-response curves of MTX for samples derived from two patients with ALL, in the absence and presence of TP (0.15 IU/mL) and XO (0.02 IU/mL) (patient A) or in the absence and presence of R75231 (1.65 μmol/L) (patient B). Both adaptations of the MTT assay did not result in dose-response curves for MTX for 11 patient samples.