Blood, marrow and heavily-bloodstained fluids are subjected to an Ammonium chloride lysis protocol. This is a low ionic strength buffer, which compromises red cell integrity, causing lysis, whilst leaving the Leukocytic fraction relatively unscathed. An unintended issue of this protocol is that, as well as destroying mature erythrocytes, it will also remove some of the later elements of erythroid differentiation, leaving an incomplete record. Hence, in cases of myelodysplasia (MDS), this may lead to slightly higher blast cells counts (i.e.: CD34+CD117+ cells) than would be discernable with morphological appraisal of a fresh, particulate smear. In any case, BSH and WHO guidelines still recommend the latter as the ‘gold-standard’ in such cases. In cases other than MDS, we have no evidence of any substantial disturbance to the population distribution in a sample. It is worth pointing out, however, that we get the best results with a fresh sample (one or two days old)- older samples, those in excess of 3 days, may show changes in population distribution that may prejudice the interpretation of cytometry results. Our experience is that bone marrow samples tend to store better than blood samples, possibly because of the relatively nourishing mix of active compounds to be found in the former. CSF samples can pose a problem for the Cytometrist. Due to the low volumes drawn and the relative paucity of cells, it is, unfortunately, the norm to be unable to collect sufficient events to be able to obtain statistically satisfactory results (NB: in the world of Cytometry, we acquire ‘events’ not cells!). In an ideal world we would prefer a sample volume of at least 5ml, although we are aware that this can be an issue for the Clinician and the Patient. Our experience with Fine Needle Aspirate (FNA) biopsy material has not been encouraging. In the main, we find they do not usually provide the numbers of cells that we would prefer to work with. As with CSF, Flow Cytometry is an unforgiving technology and low cell numbers are prejudicial to satisfactory analysis. In the event of biopsy material arriving, we do prefer larger fragments in a suitable medium (this can be saline, PBS or a tissue culture fluid, but, please, no azide, no aldehydics, and no preservative additives at all).