Interleukin-6 (IL-6) levels in cancer tissues of 32 patients with colorectal cancer were measured and analyzed in relation to the clinico-pathologic findings. The IL-6 level in cancer tissues was 81.1 +/- 118.0 pg/mg protein, which was significantly higher than the 11.2 +/- 20.8 pg/mg protein in normal colorectal tissues (p = 0.028). IL-6 levels in cancer tissues showed no correlation with the incidence of venous invasion, lymphatic invasion, lymph node involvement, or liver metastasis. The IL-6 level in cancer tissue tended to decrease as the cancer penetration extended. Our results suggest that IL-6 may play a role in human colorectal cancer growth.