During the past 10 years there has been considerable interest in the application of new technologies to identify human malignancy and predict disease outcome. Markers of cell proliferation and the technologies of flow cytometry and image analysis for the determination of DNA total content in human tumor cells have been studied in breast cancer for 20 years. In this review, the uses and limitations of these technologies for the determination of ploidy status are discussed. This review also considers the prognostic significance and potential clinical utility of ploidy measurements, S phase calculation, and individual cell cycle regulatory biomarker expression levels.