Summary A newly designed lyse-reagent for processing of whole blood samples for multiparameter flow-cytometry (MP-FCM) allows for flow-cytometrical determinations without any centrifugation during processing of samples. Comparing sample-processing by an FDA-approved lyse-reagent and by the newly designed lyse-reagent, two major advantages of the new lyse-reagent turned out: i) substantially higher recovery (about 100%) of leucocytes and ii) no selective loss of lymphocytes. Encouraged by the finding to have for determinations by MP-FCM almost all leucocytes as present in blood, MP-FCM-determinations of a particular small subset of leucocytes, namely of basophil granulocytes, have been compared to determinations of basophils, as performed by a routine haematological analyser (NE-7000). Along with a fairly good correlation (correlation coefficient about 0.8), there was no statistical significant difference in the percentages as determined by both technologies. The present data indicated that the new lyse-reagent for processing of whole blood for MP-FCM, due to the fact that leucocytes as present in blood are present for determinations by MP-FCM, may facilitate to establish MP-FCM-defined leucocyte-differential as a reference-method for the leucocyte-differential.