A decrease in the production of nitric oxide (NO) due to surgical stress has been reported. We investigated whether this decrease in NO production was related to cytokine induction and/or other clinical parameters. We therefore measured the concentrations of serum nitrite/nitrate (a stable end product of NO), serum interleukin (IL)-6, and standard clinical parameters in 13 patients undergoing major upper abdominal and thoracoabdominal surgery at preanesthesia (PRE), 2h after a surgical incision (2H), at the end of surgery (END), and on the morning of postoperative days 1 (POD 1) and 3 (POD 3). The serum concentration of nitrite/nitrate was thus found to have significantly decreased at END, POD 1, and POD 3 compared with PRE. In addition, the serum nitrite/nitrate concentration correlated negatively with the plasma lactate level, and no relationship was observed between the serum nitrite/nitrate level and either the serum IL-6 level or any other clinical parameters. Our findings thus suggest that the decrease in the serum nitrite/nitrate level might therefore be related to tissue hypoperfusion both during and after major surgery.