Image cytometric analysis of DNA ploidy status of 40 fresh primary breast carcinomas was performed in a comparative study on cytologic preparations stained directly by the Feulgen method and smears from the same tumors Feulgen-stained after Papanicolaou staining. There was a 0.82 overall concordance in diploid and aneuploid tumor classification and a good correlation (r = 0.736, P < 0.001) between the DNA indices determined by the two methods. Discordances are probably due to tumor heterogeneity. This study demonstrates that image cytometric DNA analysis on previously routine-stained cytologic preparations is feasible and reliable for pretreatment DNA analysis and suggests potential applications in retrospective studies with cytologic material from archives.