Success or failure of radiation therapy in patients with ovarian carcinoma is due to the inherent radiosensitivity of both the tumor cell and the surrounding normal tissues. The D0 value were 1.65 Gy for benign mesothelium, 1.50 for the ovarian carcinoma, and 1.45 Gy for the fibroblasts. The ovarian carcinoma cells had a similar n value (1.7) to the mesothelial (n = 2.5) or fibroblast (n = 1.2) cells. Similarly, the 24-hour potentially lethal damage repair ratios were 2.26 for the tumor cells and 2.2 for the benign cells. The kinetics of the induction and repair of DNA strand breaks caused by X-ray irradiation were similar for the three cell types.