A total of 606 consecutive patients with palpable breast lesions underwent physical examination, mammography, and fine-needle aspiration for cytologic and flow-cytometric (FCM) DNA analyses. FCM determinations included DNA ploidy and the fraction of cells in S + G2 + M phases. Aneuploid clones were considered indicative of malignancy; diploid, rapidly proliferating (S+G2+M>12%) clones were considered suggestive of malignancy; and diploid, slowly proliferating clones were considered indicative of benignancy. Sensitivity, specificity, and the predictive accuracy for positive or negative results of FCM information were 82%, 90%, 93.1% and 69.8%, respectively. These values were lower than those observed for the three conventional diagnostic assays owing to the presence of false-positive results (in 23 cases) or unassessable DNA plots (in 90 cases). FCM information alone detected five cases in which the other tests gave inconclusive results and in association to the conventional diagnostic triple test, increased the incidence of positive conclusive cases from 97.9% to 99.2%. However, further refinements are needed before this approach can be used as a routine diagnostic tool.