DIA allows quantification of nuclear DNA content that may aid in distinguishing benign from malignant biliary tract strictures. Methods: The Mayo Clinic pathology databank was used to identify all biliary brush cytology specimens obtained between 6/97 and 6/99. Corresponding medical records were reviewed to determine whether patients had malignant or benign biliary strictures. A stricture was classified as malignant if proven by biopsy or surgery, and as benign if confirmed by surgery or a cancer-free clinical course for ≥ 1 year. Strictures were further classified into benign strictures with negative brush cytology (Group 1), malignant strictures with negative brush cytology (Group 2a- pancreatic carcinoma, Group 2b- cholangiocarcinoma), and malignant strictures with positive brush cytology (Group 3). A significant number of specimens were not available for analysis, as they were prepared on filters. Pap-stained smears of available brush cytology specimens were de-stained and then re-stained using Feulgen dye. A maximum of 200 nuclear images were quantified for DNA content without knowledge of stricture type. DNA histograms were generated and ploidy results compared with the class of stricture. Results: 25 specimens were analyzed (see table). Assuming the presence of any aneuploid cells indicating malignancy, the sensitivity of DIA was 85%, accurately predicting a malignant stricture in 13 of 16 samples. Conclusions: 1. Ploidy assessment by DIA has the potential to greatly enhance the sensitivity of diagnosing malignant strictures compared to routine cytology alone. 2. Additional studies will be needed to further assess the specificity of DIA in a broad range of benign inflammatory lesions.