Detection of measurable residual disease (MRD) has been shown to an important predictor of relapse in patients with paediatric leukaemia. Residual disease may be detected by several methods including multiparameter flow cytometry. The detection of MRD by multiparameter flow cytometry depends on identifying leukaemia associated immunophenotype and also being able to distinguish leukaemic cells from normal populations in the marrow. New therapies targeting CD19 and CD22 have provided additional challenges to routine MRD testing in Acute Lymphoblastic Leukaemia necessitating the development of alternative panels and gating strategies. Examples will be worked through in the session.