“…In addition, there was no correlation between the S-phase of the neoplastic and normal bone marrow cells (r = 0.22; P > 0.10); this work therefore shows that the assessment of the total proliferative rate of bone marrow samples does not reflect either the proliferation of normal cells or that of neoplastic plasma cells but will depend on the proliferative rate and the percentage of each population within the sample, which can be assessed by the technique described here. Key terms: Flow cytometry, DNA ploidy, cell cycle, S-phase, multiple myeloma Quantitative measurements of tumor cell DNA content using flow cytometry (FCM) have been performed for over two decades (1,9,10,25,26,28,39). These studies have basically provided two different types of information on the biology of neoplastic cells: (1) the existence or absence of clonal abnormalities in cell DNA content, DNA aneuploidy, and (2) the analysis of the distribution of a certain cell population through the different cell cycle phases.…”