We studied p53 expression in 46 colorectal carcinomas by immunohistochemistry. We examined the relationship between p53 expression and the pathological findings, the prognosis and tumor proliferative activity by Ki-67 staining or DNA ploidy pattern using an image cytometer. Expression of p53 was observed in 41.3% of carcinomas. No correlation was found between p53 expression and the depth of invasion, lymph node metastasis or Dukes' stage. No difference in survival was found between p53 positive and negative patients after curative surgery. We also studied the DNA ploidy pattern using an image cytometer in 28 carcinomas. Aneuploidy was found more frequently in the p53 positive areas than in the negative ones, but there was no significant difference. The DNA index showed no difference between the p53 positive and negative areas. We examined proliferating activity using Ki-67. There was no difference in the Ki-67 labeling index between p53 positive and negative areas. In the present study, there was no correlation between p53 expression and pathological findings, prognosis, tumor proliferative activity using Ki-67 staining or DNA ploidy pattern. Thus, p53 expression was suggested to have little relationship to grade of malignancy.