Quantitative DNA measurements were performed in 183 colorectal carcinomas by image and flow cytometric analyses of paraffin-embedded tissue. Flow cytometric analysis yielded more diploid tumors compared with image analysis, which identified more tetraploid tumors. Histogram patterns were concordant in 115 tumors (66%); the discordant cases were primarily tumors interpreted as diploid by flow cytometric analysis but were aneuploid or tetraploid by image analysis. Linear regression analysis of DNA indices of concordant samples showed good correlation but only moderate correlation for the entire group. Both techniques revealed more aneuploid tumors in the distal colon and rectum than in the proximal colon. Diploid tumors were associated with a better prognosis; however, tetraploid tumors behaved like aneuploid tumors by flow cytometric analysis but like diploid tumors by image analysis. When stratified by stage, the prognostic value of diploid tumors was seen in stages A and B disease by image analysis only and in stage C disease by flow cytometric analysis only, possibly because of the small cohort size. The S-phase fraction (mean value, 16.8% +/- 9.9%) was higher in aneuploid than in diploid tumors, but no relationship to prognosis was seen. Flow cytometric and image analyses are useful to study ploidy of colorectal carcinoma from archival material. However, important discordant observations reflecting differences in characteristics of the two techniques should be considered, depending on which technique is used.