DNA ploidy and S phase fraction analysis by flow cytometry on breast and ovarian tumor cells continuously exposed to aloin, a natural anthraquinone, at two concentrations (20-60 microg/ml) was done. Untreated breast and ovarian tumor cells (control) showed an aneuploid pattern, with a mean DNA index of 2.10+/-0.10 and S phase fraction of 28.46+/-1.5 and 17.40+/-0.75%, respectively. Treatment of breast and ovarian tumor cells with aloin showed a persistent aneuploid pattern and a significantly dose-dependent increase in the percentage of S phase fraction and in the proportion of cells cycling at a higher ploidy level (>G2M). The polyploidization indicates that aloin does not inhibit initiation of DNA synthesis and that cells replicated a full complement of DNA but had difficulty in M phase.