A study was conducted to clarify the quantitative relationship between the alteration of protein metabolism and the severity of surgical stress to further understand the mechanisms of body nitrogen losses in surgical trauma. Twenty-one patients undergoing esophagectomy for esophageal cancer (group E), and 22 undergoing gastrectomy or colorectal operations for gastric or colorectal cancer (Group GC) were studied. All patients were fed exclusively by parenteral nutrition (PN) providing 1.5 g protein.kg-1.d-1 and 35 kcal.kg-1.d-1 before and after the operation. The measurements of whole-body protein turnover, synthesis, and breakdown were performed preoperatively and on postoperative days (PODs) .3 and 10. Urinary excretion of total nitrogen and total catecholamines was also measured. Urinary excretion of the total catecholamines of group E was twice as high as that of group GC on the POD 3 and well reflected the severity of surgical stress. Negative correlation of nitrogen retention to urinary excretion of the total catecholamines was also observed (r = 0.64; P < 0.01). The correlations between the urinary excretion of the total catecholamines and the whole-body protein flux, synthesis, and breakdown were statistically significant (r = 0.57, 0.27, and 0.57, respectively; P < 0.01 in all). Rate of elevation in breakdown according to the stress level was greater than that of synthesis. Consequently the progressive aggravation of nitrogen balance according to the severity of surgical stress was observed.