ST3Gal1 is a sialyltransferase, an enzyme that adds the sugar sialic acid to chains of other carbohydrates. It has an affinity for the disaccharide, Thomsen-Friedenreich Antigen (TF-Ag), a tumor-associated carbohydrate prevalent on many types of tumor cells, and preferentially adds sialic acid to TF-Ag. TF-Ag is involved in tumor cell metastasis. Previous research found that differential up-regulation of ST3Gal1 expression in a nonmetastatic breast tumor cell line in comparison to a related metastatic breast tumor cell line. This research aims to: 1) clone the involved ST3Gal1 cDNA, 2) add it to the metastatic cell line, and 3) determine changes in cell adhesion and metastatic potential in vitro. TF-Ag is in a cryptic form in normal cells due to masking by sialic acid residues, where as in cancer cells it is not masked. TF-Ag binds to molecules on the inside of blood vessels, helping the tumor cells migrate to other organs, thus playing a role in metastasis. Metastatic potential can be measured in an animal model, but this research includes attempts to optimize an in vitro model in which cells from blood vessels are grown in culture and their binding to tumor cells measured.