A new technique for transplanting duct-ligated rat pancreas grafts, rather similar to the technique for spleen grafting in rats, is presented. Inbred AGUS and WAG rats with a strong Ag-B incompatibility were used. Duct-ligated pancreas AGUS to AGUS isografts survived indefinitely in streptozotocin-induced diabetic hosts while WAG to AGUS allografts were quickly rejected. However, when WAG spleen and pancreas were transplanted en bloc to AGUS rats, endocrine pancreas graft function persisted for up to 6 weeks. This finding of a transient protection of pancreas allografts by donor-strain spleen allografts led to further experiments. AGUS recipients first received WAG spleen allografts which then were removed after 3 to 5 months, at which time WAG pancreas allografts were inserted. Sixty-eight per cent of these grafts survived and cured their hosts of streptozotocin-induced diabetes.