In this study, the changes of protein kinetics in patients with gastric cancer were determined using by 15N-glycine tracer assay before and after parenteral nutrition. The results showed that the protein turnover especially anabolic rate may be enhanced by parenteral nutritional support. The pre- and post operative increase of protein anabolic rate was more than that of the catabolic rate, about 10% and 88% respectively. This phenomenon could be explained as following, (1). the abnormal metabolism in cancer patients was extinguished after the tumor resection; (2). the supplementation of the nitrogen was increased; (3). branched chain amino acids could be used as energy resource for muscle metabolism and to improve protein synthesis while its breakdown was inhibited. CONCLUSIONS It is necessary to administer the parenteral nutritional support to patients with malnutrition before operation. With adequate nitrogen and calorie supply, negative nitrogen balance could be improved.