Peri-operative serum levels of interleukin-6 (IL-6) were determined in 62 patients who underwent resection of colorectal cancer to clarify the relationship between nutritional status and IL-6 response. Patients were divided into two groups based on creatinine height index: malnourished group (n=13) and normally nourished group (n=49). The preoperative median serum level of IL-6 in the malnourished group was significantly higher than in the normally nourished group (P=0.041). The postoperative median serum level of IL-6 in the malnourished group also tended to be higher. In conclusion, the peri-operative IL-6 response may be activated in malnourished colorectal cancer patients.