volume of each of the cell populations of interest may be determined and from that the absolute count for each in the first example the cellbeads are obtained by simultaneously staining and fixing normal human leucocytes with a propidium iodide paraformaldehyde solution unlike synthetic beads the human cellbeads behaved similarly to normal cells during cell lysis and cell washing procedures when known number of cellbeads were added to whole blood samples and the numbers of cellbeads and lymphocytes determined highly reproducible and accurate enumerations were obtained which were far more so than when using synthetic beads whole blood 16 ml was collected from a normal volunteer into four 5 ml vacutainers containing edta anticoagulant aliquots 1 ml were added to four sterile 25 ml plastic screwcap tubes sarstedt ltd leicester u k containing 20 ml of lysing solution the contents were mixed then left for 10 min at room temperature following centrifugation at 300 g for 5 min the supematants were discarded the peripheral blood mononuclear cell pbmc pellets were then resuspended and combined into one tube to which further pbs 15 ml was added this process was repeated a further three times all the pbmc aliquots were then pooled before being redivided into four tubes these were again centrifuged at 300 g for 5 min and the supernatants discarded the cells in each tube were resuspended in freshly diluted propidium iodide dye fixation solution 5 ml and left at 4 u00b0 c overnight.