Samples from 14 human colorectal carcinomas were analysed by means of classical (one-parameter) flow cytometry. (S+G2)-phase fractions were calculated from DNA histograms with the help of two different algorithms. At the same time, the percentage of cells positive for the Ki-67 antibody, which recognizes proliferating cells, was determined in cytocentrifuge preparations. Significant correlations between the two indices were found only if the histogram analysis included background subtraction and aggregate correction. This finding may throw some light on the reliability of prognosis based on flow cytometry.