The Transplantation and Electron Microscopy Unit provided electron microscope facilities for the Hall Institute Units and for other Institutions. It also had a research wing, which initially concentrated on pancreatic islet transplantation in mice with induced diabetes mellitus. The Unit attempted a small clinical transplantation trial in selected human patients beginning in 1983/84, but it progressed slowly due to a poor supply of immature human pancreas. Initial transplants yielded no evidence of graft function after two years so the Unit returned to a focus on animal models in 1987/88. The acquisition of a NOD (non-obese diabetic) mouse model in 1984/85 greatly expanded opportunities for transplantation studies relevant to human type I insulin-dependent diabetes mellitus (IDDM). The NOD mice proved invaluable for studies in immunosuppression, graft rejection and immuno-isolation, and for researching xenotransplantation of islets from foetal pig pancreas into NOD mice. This work was first undertaken in 1986 and became the Unit's main focus by 1991/92. In 1994/95 xenotransplantation studies were extended to primates, but an absence of primate autoimmune insulin-dependent diabetes mellitus (IDDM) prevented a study on recurrence of the disease after transplantation.