The pattern of intra-tumor DNA ploidy distribution was analyzed in stepwise sections in 64 cases of surgically resected gastric carcinoma. Five varying patterns were identified: Type A comprised only diploidy in all stepwise sections, Type B comprised only aneuploidy with the same DNA Index(DI), Type C comprised diploidy in the great majority of sections with aneuploidy in some parts, Type D comprised aneuploidy in the great majority of sections with diploidy in some parts and Type E comprised only aneuploidy, but with varying DI. These 5 patterns could be grouped into 2 categories; predominantly diploid (Types A and C) and predominantly aneuploid (Types B, D and E). The former category included 34 cases (12 differentiated carcinomas) while the latter included 30 cases (22 differentiated carcinomas). Thus, a statistically significant correlation was detected between the histologic type and the intra-tumor DNA ploidy distribution pattern; in the majority of cases, differentiated carcinoma exhibited predominantly aneuploidy, while undifferentiated carcinoma exhibited predominantly diploidy (p less than 0.01). This tendency was the same for all depths of invasion, except for submucosal carcinomas which exhibited predominantly diploidy.