Demonstrating sterility, purity, identity and potency of a medicinal product are critical requirements to qualify its use in patients/human subjects.  The clinical use use of flow cytometry is extremely widespread in the analysis of patient blood samples and during the manufacture of ATMP.  There is, however, a large amount of variability in the operation of flow assays across different institutions and, sometimes, operators within the same institution.  The ATTCs convened a workshop of experienced practitioners and regulators to develop a consensus of what ‘good practice’ looks like and to understand the key parameters for use of flow cytometry as part of QC.  The flow workshop held 27th February at Royal Pharmaceutical Society (London) was attended by 43 people for 19 different organisations covering the NHS, academic and commercial developers, regulators and standards organisations