The significance of a preoperative elevation of serum C-reactive protein (CRP) as an indicator of the malignant potential and prognosis in colorectal cancer is reported. The reduction of circulating lymphocytes reflects the immunosuppressive conditions of patients with neoplasms. The aim of the current study was to elucidate the significance of a preoperative elevation of serum CRP as an indicator of the impaired immunity of the patients with colorectal cancer. The subjects were 155 consecutive patients with colorectal cancer who were treated with surgical resection. The preoperative serum CRP level and the proportion of circulating lymphocytes in peripheral blood were measured and the relationship between these values was investigated. The mean value of lymphocytes percentages in patients with the preoperative elevation of serum CRP was 25.2 +/- 8.7%, which was significantly lower than that (33.4 +/- 9.3%) in patients without the preoperative elevation of serum CRP (p < 0.01). In summary, preoperative elevation of serum CRP was significantly related to the reduction of lymphocyte percentages in peripheral blood, and it can be an indicator of impaired immunity in the patients with colorectal cancer.