Autologous transfusions of 111indium-labelled peripheral blood lymphocytes reportedly image the pancreas of patients with Type 1 (insulin-dependent) diabetes at the time of onset. We attempted to apply this technique to the spontaneously diabetic BB/W rat. First, acutely diabetic BB/W rats, diabetes-prone BB/W rats, diabetes-resistant W-line BB/W rats, and Wistar Furth rats were given autologous transfusions of labelled peripheral blood lymphocytes. Radioactivity recovered from the pancreas was similar in all groups. No correlation was found between the intensity of imaging and the presence or intensity of insulitis. To decrease non-specific intravascular radioactivity, acutely diabetic, diabetes-prone, and W-line rats were perfused 48 h after autologous transfusion of labelled lymphocytes. Again, the intensity of recovered activity was similar in all groups, using both macroautoradiography and numerical counting techniques. A second set of experiments studied diabetes and insulitis induced by passive transfer of concanavalin A-treated splenic lymphocytes from acutely diabetic donors. Activated lymphocytes were labelled with 111Indium and given to groups of diabetes-prone and diabetes-resistant rats. There were no differences in pancreatic localization 72-96 h after injection. Groups of diabetes-prone and diabetes-resistant rats were also given concanavalin A-activated lymphocytes and then challenged 2-10 days later with autologous transfusions of labelled peripheral blood lymphocytes. Again, no differences in organ labelling or imaging were detected. We conclude that the autologous transfusions of 111indium-labelled lymphocytes do not label or image the pancreas of the BB/W rat.