Measurements of DNA ploidy, proliferation index and nuclear area were performed on 210 samples taken from 15 human colorectal tissues. The tissues were divided into four groups labeled G1, G2, G3 and C. For each of the 15 tissues 9 samples were taken from the so-called unaffected--i.e., marginal--mucosa (G1-G3 groups) and 5 from the tumor (C group). The 9 samples from the unaffected mucosa of each tumor were obtained at a distance of 10 cm (3 samples/tissue, G1 group), 5 cm (3 samples/tissue, G2 group) and 1 cm (3 samples/tissue, G3 group) from the tumor. Computerized cell image analysis was carried out on Feulgen-stained cell suspensions obtained from paraffin-embedded, formalin-fixed tissues. The results revealed that four to five analyses are necessary to detect minor aneuploid cell nuclei populations in human colorectal tumors. A definite homogeneous diploid pattern was found in the G1-G3 samples. In contrast, proliferative activity varied widely between the normal and tumor samples, with such variations observed at both the sample-to-sample and tissue-to-tissue level. The nuclear area also varied markedly across the samples from a given tissue--i.e., both marginal and tumoral and across the tissues themselves. Finally, we observed that the diploid tumors, the nuclear sizes of which varied as widely as those of the aneuploid tumors, possessed a higher proportion of highly proliferating samples than did the aneuploid.