Flow cytometry is being used as an aid in planning the treatment of patients with various malignancies. We report our experience with DNA content analysis on paraffin-embedded carcinomas. Hospital, radiation therapy, clinic, and pathology records were reviewed in 139 cases of endometrial carcinoma diagnosed between December 1980 and December 1986. Patients having Stage IV tumors, endometrial sarcomas, dual primary tumors, or incomplete records were eliminated from the analysis, which left 98 evaluable patients. This report outlines our experience with the first 20 patients. Five of 20 (25%) specimens demonstrated DNA content consistent with aneuploidy, median coefficient of variance of 5.3%. The median survival time of these five patients is 55 months, with three dying of cancer and one patient dying of other causes but with metastatic disease. The median %S phase was 3.7% in the 15 patients comprising the DNA content diploid population, median coefficient of variance 5.4%. No patient whose tumor showed S-phase cells below 3.7% died of endometrial cancer. Four of 7 patients developed recurrent cancer with 3 of the 4 patients dying of disease in the high %S phase group. The median patients survival time in the DNA content diploid population was 73 (range: 17-98) months. Patients with 3.7% or below S-phase cells had a median survival time of 75 (range: 40-98) months whereas the median survival time was 48 (range: 17-89) months for patients having a %S phase fraction above 3.7%. Although the number of patients studied is small, it appears that DNA content aneuploid tumors are frequently "upstaged" at surgery. These patients may not benefit from preoperative irradiation. Accurate determination of the %S phase fraction in DNA content diploid tumors may possibly identify patients with a poorer prognosis who may benefit from adjuvant therapy.