Quantitative DNA analysis was performed on preoperative fine needle aspirates of 12 breast cancers and 1 benign lesion using the Cell Analysis Systems (CAS) Model 200 image analysis system. The smears were prepared on CAS slides, routinely processed for Papanicolaou staining, and then destained and restained with Feulgen stain after cytologic evaluation. Four cases were DNA diploid, 3 were tetraploid, 1 was diploid/tetraploid, and 5 were aneuploid. When compared to analysis of samples from the resected tumor, both DNA index and S-phase fraction were constant.