Mucins are large glycoproteins that form a protective layer along the lumens of the organs of the gastrointestinal and reproductive tracts. Frequently in tumors of the pancreas there are changes in the structure of mucin carbohydrates and/or levels of apomucin types. Originally mucins were of interest clinically because diagnostic tests could be based on their levels in circulation. More recently mucin directed monoclonal antibodies have been used to target tumors with cytotoxic agents. There is now a considerable literature on the development of mucin-based vaccines. Both monoclonal antibodies and vaccines could be powerful tools to specifically target tumor cells in distant metastases. Gene therapy based upon the MUC1 gene promoter is being investigated to target therapeutic genes to MUC1 expressing cells. The carbohydrates of mucins on the surface of tumor cells have been reported to inhibit cells of the immune system. These carbohydrates also act as ligands during the process of tumor cell metastasis. Another approach to therapy is to block interactions between the ligands and their receptors.