Flow cytometry offers a relatively simple method to determine the DNA content of colorectal cancers. However, the technique can not discover minor changes in karyotype which may characterize near-diploid tumors, nor will it detect very small populations of aneuploid cells. In an attempt to improve the detection of such cells, we incubated biopsy material prior to analysis. This method revealed an aneuploid subpopulation in one of two biopsies studied. This simple protocol may ultimately lead to a more accurate assessment of the ploidy in colon cancer.