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Dexamethasone (dex) is a key treatment for childhood acute lymphoblastic leukaemia (ALL), but is associated with significant variability in terms of toxicity and efficacy. In this project, the following variables were assessed to better understand how dex personalisation may be achieved: pharmacokinetics, intracellular dex accumulation, glucocorticoid receptor (GR) posttranslational modifications and B-cell maturation state. For pharmacokinetic studies, samples were collected from 154 patients randomised to short (10mg/m2 x 14 days) or standard (6mg/m2 x 28 days) dex induction therapy, as part of the UKALL 2011 trial, and analysed using a validated LC/MS method. Wide pharmacokinetic variability was observed, with AUC0-12h and Cmax significantly higher on the short compared to standard arm. However there was substantial overlap between the two arms, with a number of patients on the standard arm exhibiting higher exposures than those on short therapy. The UKALL 2011 trial found no statistical difference in terms of steroid-related toxicity or MRD response between short and standard dosing. These data suggest that the considerable dex pharmacokinetic variation identified may be a more important factor than variation in dosing regimen. For cellular pharmacology experiments, cell lines, primagraft and primary patient samples were studied. Dex sensitivity was assessed using Alamar Blue assays and GI50 values ranged from 2-1000nM. Western blotting indicated wildtype GR in all samples. Dex accumulation was assessed by LC/MS and flow cytometric analysis of dex-FITC. While patient samples exhibited large variability, dex accumulation was not significantly different between sensitive and resistant cells. Differential dex sensitivity was not accounted for by differences in GR posttranslational modifications, assessed using capillary isoelectric focusing. However, assessment of B-cell maturation using mass cytometry revealed a relationship with dex resistance. Importantly, >50% of patient cell samples had dex GI50 values greater than plasma concentrations observed on either arm of the UKALL 2011 trial. A combined approach incorporating pharmacokinetic assessments and cellular response in ALL cells may allow a more comprehensive understanding of dex pharmacology to optimise its clinical utility.