Surgically resected specimens of 139 cases of large-bowel carcinoma were analysed in this study. Each carcinoma was cut out in stepwise section through the whole tumor, and flow cytometric DNA measurement was performed for each section. The intratumor DNA ploidy distribution pattern decided in this way was classified into 5 types (Type A-E). The 139 cases of carcinoma comprised 19 cases of Type A, 27 Type B, 11 Type C, 37 Type D and 45 Type E. The intratumor DNA ploidy distribution pattern showed a statistically significant correlation to tumor size, gross type, depth of invasion, growth pattern at the tumor margin, venous permeation of visceral wall, DNA Index and Dukes stage. Among these 5 types of carcinoma, carcinoma showing Type E was seen most frequently, even in the earlier stage, and found most frequently among the cases showing invasive growth pattern at the tumor margin, positive venous permeation in the visceral wall and DNA Index of more than 1.7. Therefore, the intratumor DNA ploidy distribution pattern seemed to reflect the degree of tumor malignancy as well as that of tumor advancement. Moreover, Type E pattern of carcinoma appeared to reveal the highest grade of malignancy, and early detection of this type seemed to be necessary in order to improve survival after surgery.