DNA and proteins of ethanol fixed cells are simultaneously analysed by cytofluorimetry in 35 cases of adult acute leukemias. DNA is coloured by propidium iodide and proteins by FITC. These technics allow to know the GO/G1, S, G2 + M cell-cycle phases and the protein cell content for each phase. We also can evaluate the fraction of low protein content cells (LPC fraction) that seems to be the GO and early G1 fraction. A good correlation exists between the percentage of S phase cells and the LPC fraction. This parameter, because of its important dispersion, must have a better discriminating value than S phase, especially for the prognosis analysis. Furthermore acute myeloid leukemias have a protein content that varies with the cytological maturation. Therefore, P1 + FITC colorations would give quantitative criteria for the acute leukemias cytological analysis and their prognostic valuation.