Isolated monoclonal antibodies are disclosed herein that specifically bind a cell surface antigen expressed on the human pancreatic endocrine cells or a subset thereof, and/or a precursor thereof. Isolated monoclonal antibodies are also disclosed herein that specifically bind a cell surface antigen expressed on human pancreatic exocrine cells or human ductal cells. Humanized forms of these antibodies, and functional fragments of these antibodies, are also disclosed. The antibodies can be conjugated to an effector molecule, such as a detectable marker, a therapeutic agent, or a toxin. These antibodies are of use to detect and isolate pancreatic cells or a subset thereof. The antibodies can be used for in vitro or in vivo detection and/or isolation of pancreatic endocrine cells. Methods of treating a pancreatic tumor are also disclosed. In several examples, the isolated monoclonal antibodies bind pancreatic endocrine cells and can be used to detect diabetes or a pancreatic endocrine cell tumor.