Multiparameter flow cytometry can allow for accurate lineage assignment of leukaemia cell populations in approximately 99% of cases, whereby the emphasis lies in the word 'can'. Despite the fact that the very few markers that are lineage-specific are localized inside the cell (e.g. myeloperoxidase, lactoferrin, cytoplasmic CD3, cytoplasmic CD22), several investigators still shy away from including these essential test elements in their routine panels. Of course, the staining of intracellular antigens requires the added effort of determining optimal conditions. Published suggestions often need to be revised, and cell lines must be used as positive and negative controls. The same holds true for other new and exciting applications of flow cytometry, such as the monitoring of minimal residual disease (MRD) or the establishment of physiological assays (e.g. measuring the activity of drug-efflux pumps). The beauty of-and unfortunately for some, the problem with-multiparameter flow cytometry is that although immunophenotyping by flow cytometry has become a routine approach to the diagnosis of haematological malignancies it is a discipline that is still in development. New antibodies are continually being introduced and new diagnostic and prognostically relevant subtypes are being published in almost every issue of the major scientific journals. It is therefore very important for the flow cytometrist not only to strive for optimal performance of all tests employed but also to keep up with new knowledge and to incorporate it into the interpretation of routine specimens. We owe it to our patients to diagnose their disease accurately and in accordance with accepted standards of interpretation so that the treating physicians can trust immunophenotyping results and act accordingly in the management of their patients.