The nuclear areas, perimeter, diameter and form factor, and nucleolar area and diameter of about 50 cells in each in 38 colonic epithelial lesions including normal epithelium (6), Peutz-Jeghers polyp (2), adenoma (11), dysplasia (6) and carcinoma (13) were measured at the electron microscopic level by using an image analyzer. The area of nucleoli was larger in dysplasia and carcinoma than the normal (statistically significant). The area of nuclei was larger in carcinoma than the normal. The form factor was also largest in the nuclei of carcinoma, indicating that these cells had the most spherical shape. These results suggest the possibility of quantitative diagnosis of epithelial lesions by measuring the area and perimeter of some 50 nuclei and nucleoli.