DNA content analysis is a routine test in most laboratories involved in the tumor assessment and in the cell cycle analysis. In the experimental approach this procedure is already well established, while in the solid tumor analysis has to be implemented to obtain more significant results from the clinical point of view. Cell suspensions from solid tumors are in fact very often "contaminated" by other cell types such as stromal cells, leukocytes etc. Accurate proliferation studies therefore require to exclude these contaminating elements from the analysis. Actually many proliferation markers (PM) both endogenous (PCNA, Ki67, cyclins etc.) and exogenous (BrdU) can easily be quantified by flow cytometry. Correlated dual parameter analysis DNA/PM allows detailed proliferation studies in both experimental and clinical oncology. The possibility to "drive" these dual parameter acquisitions by a third marker able to focus (cytokeratins) or to exclude (CD45) specific subpopulations from the analysis will improve the clinical significance of the acquired data. Finally, very important at clinical level are the problems related to the standardization of the methodologies. The availability of stabilized reagents allows to obtain very reproducible results that is one of the most important steps of all the analytical procedures.