The results of flow cytometric analysis of ploidy and S-phase fraction for invasive breast cancers have been compared with various clinical and pathologic parameters by many investigators. Ploidy usually has been found to be associated with histologic type, tumor grade, and S-phase fraction values, but not with patient age, menopausal status, tumor size, axillary nodal status, estrogen receptor status, or progesterone receptor status. S-phase fraction values have correlated with histologic type, grade, estrogen receptor status, and progesterone receptor status, but not with menopausal status or axillary nodal status. Although in several studies ploidy and S-phase fraction have been compared with patient outcome, only a few of these reports have stratified data according to the histologic types and grades of the neoplasms. There is conflicting information regarding the value of ploidy analysis for women with either node-negative or node-positive breast carcinoma. Data from a few studies seem to indicate that S-phase fraction alone or in combination with ploidy may be more important prognostically than ploidy alone, although the results have not been uniform. More studies that examine ploidy, S-phase fraction, various important clinical and pathologic variables, and outcome for patients with invasive mammary cancer must be performed before the clinical importance of DNA analysis by flow cytometry becomes known.