Autoimmune diabetes can be transferred to young, diabetes prone BB/W rats by injecting them intravenously with concanavalin A (Con A)-treated spleen cells from acute diabetic BB/W donors. This study describes the transfer of diabetes to the normal Wistar-Furth strain of rats using a similar procedure. For the successful transfer of diabetes it was necessary to immunosuppress recipient animals with a single intraperitoneal injection of cyclophosphamide 24-48 h before administering Con A-stimulated spleen cells from acute diabetic BB/W rats. Of 68 Wistar-Furth rats in immunosuppressed with a dose of 100-150 mg cyclophosphamide/kg body wt, 10 (15%) became diabetic. None of the control rats receiving either Con A-stimulated Wistar-Furth spleen cells (n = 28), freshly isolated BB/W spleen cells (n = 14), or fresh RPMI medium (n = 11) became diabetic. These data indicate that diabetes can be transferred from BB/W to Wistar-Furth rats. In addition, they support the hypothesis that cell-mediated immune processes are involved in the development of insulin-dependent diabetes and rule out any absolute requirement for BB-derived genes in the target pancreatic beta cells.