Image cytometric determination of DNA content was performed on 207 colorectal adenocarcinomas surgically resected from 205 patients. Of these 207 tumors, 193 (93.2%) showed an aneuploid DNA distribution pattern, whereas the remaining 14 (6.8%) exhibited a DNA pattern corresponding to that found in proliferating diploid populations. The DNA content of 20 of these colorectal carcinomas was also studied by flow cytometric measurements on deparaffinized, disintegrated material. Flow cytometric measurement detected aneuploidy in only 9 of these 20 (45%) tumors, whereas 17 of the same 20 (85%) carcinomas showed aneuploidy when using image cytometric measurement on imprints. These results suggest that colorectal carcinomas are either aneuploid (vast majority) or proliferating diploid and that image cytometric DNA measurement on histologically controlled material is superior to flow cytometric measurement.