Effects of etoposide on the cell deaths of a human pancreatic cancer cell line by exposure to high-dose X-ray irradiation were examined. Both high dose X-ray irradiation and etoposide killed the pancreatic cancer cells by apoptosis. With 30 gray irradiation, simultaneous treatment of etoposide did not alter the percentage of cell deaths; however, 24-hr prior treatment of etoposide killed a significantly larger percentage of the cells, accompanying the accumulation to the S phase of the cell cycle. The results indicate that apoptosis of human pancreatic cancer cell line induced by high dose X-ray irradiation can be enhanced by prior treatment with etoposide.