Analysis of endometrial carcinoma of 15 cases and the normal endometrium from 12 control cases was made using flow cytometry. The proliferative activity and the ploidy level of the tumors were determined and a comparative study of the tumors classified by the nuclear grade of the tumor was made. In comparison with normal endometrium, endometrial carcinoma tissue had a significantly larger S-phase fraction of the cell cycle. Moreover, among the endometrial carcinoma cases, the percentage of S-phase cells was found to increase with increases in abnormalities of nuclear morphology. Endometrial carcinoma cases had higher levels of G2+M phase fractions than normal endometrium, but not significantly so. The proliferation index of endometrial carcinomas was significantly higher than that in normal endometrium, and it was found that proliferative activity became more robust the more irregular the nuclear morphology. With regard to the ploidy level, all of the normal endometria and Nuclear Grade 1 or 2 endometrial carcinoma cases showed a DNA distribution between diploid and tetraploid. In contrast, Nuclear Grade 3 cases could be subdivided into two groups, one which had a DNA distribution between diploid and tetraploid with an extremely high proliferation index and the other which had an aneuploid DNA stem line.