The goal of this project is to develop a monoclonal antibody-based imaging reagent capable of visualizing human parathyroid glands. Phase I studies will be directed to isolation and characterization of human parathyroid-specific mouse monoclonal antibodies and preliminary analysis of their target antigens. Secondly, because the class and sub-class of antibodies will likely influence imaging properties, variants of hybridomas will be selected by fluorescence activated cell sorter that secrete immunoglobulins of different IgG subclasses and IgM. These antibodies will be tested for localization of human parathyroid fragments in nude mice. Phase II studies will likely focus on the imaging parameters of these variant antibodies in large animals, such as dogs or monkeys, to select the optimal conditions for imaging in humans.