Accumulation of ubiquitin (Ub) has been documented in various cancers. The levels of the two forms of Ub, i.e. free ubiquitin (FUb) and multi-ubiquitin chain (MUC) were measured in colorectal cancers and in matched normal colonic tissues in 43 patients. When compared to normal colonic tissues, the levels of both FUb and MUC were significantly higher in the cancerous tissues (P < 0.01, respectively). The level of FUb was related to the depth of invasion (P < 0.05). The level of MUC was related to blood vessel invasion and lymphatic vessel invasion (P < 0.05). The levels of FUb and MUC had no correlation with histological grade, lymph node metastasis, liver metastasis or relapse-free survival. We conclude that the levels of FUb and MUC were up-replated in colorectal cancer and were correlated with the pathological findings. (C) 2004 Elsevier Ireland Ltd. All rights reserved.