Mucins are high molecular weight glycoproteins which are heavily glycosylated with many carbohydrate side chains. In epithelial cancers such as colorectal cancer, both qualitative and quanti-tative alterations in carbohydrate and polypeptide moieties of mucin glycoproteins occur. These changes in mucin glycoproteins are one of the most common phenotypic markers of colorectal carcino-genesis and may play an important pathobiological role. The expression of some of the sialylated carbohydrate antigens appears to correlate with a poor prognosis and increased metastatic potential in colorectal cancer. The increased exposure of peptide epitopes of mucin glycoproteins in colorectal cancer appears to be due to either abnormal glycosylation and/or altered levels of mucin gene tran-scription. In addition, dysregulation of tissue specific mucin genes occurs in colorectal cancers. This information is currently being exploited for further elucidation of the molecular mechanisms involved in carcinogenesis, tumor progression and metastasis, and the development of novel methods of colo-rectal cancer diagnosis and therapy.