|| We investigated the diagnostic significance of IL-6 for lymph node metastasis and/or hepatic metastasis from colorectal cancer in 65 patients and evaluated the contributions of 8 factors (IL-6, HGF, IL-1beta, TNF-alpha, TGF-beta1, ELAM-1, ICAM-1, VCAM-1) toward Dukes.s classification of 53 patients. We also examined IL-6 expression in tumor tissue. From the receiver operating characteristic (ROC) curve analysis, an optimal cutoff value of 5.8 pg/ml was determined to classify lymph node and/or hepatic metastasis, and that of 6.3 pg/ml was determined to classify hepatic metastasis. These values indicated sensitivities of 55.0% and 71.4%, and specifi cities of 100% and 88.6%, respectively. IL-6, HGF, and ELAM-1 were very useful for distinguishing among Dukes.s A/B group, C group, and D group. In all cases with high IL-6 values (more than 25.0 pg/ml), immunohistochemical staining was positive for IL-6 in the cytoplasm of cancer cells. IL-6 is strongly suspected to be involved in lymph node and/or hepatic metastasis by promoting it through HGF, and serum IL-6 value (pg/ml) would be useful diagnostically to estimate whether or not there is a high risk of lymph node and/or hepatic metastasis.