Between 7 and 18 wk after transplantation, the insulin contained in duct-ligated, pancreas transplants increased twofold whereas glucagon content showed no significant change. Insulin contents of the recipient's own endogenous pancreas, though severely depleted after streptozotocin injection, also showed a twofold increase. The combined insulin reserves in transplant in mice at 18 wk which totaled 30% of that in aged-matched, normal controls was still insufficient to promote normal tolerance and insulin response to intravenously injected glucose. In a second experiment reported herein, we found that the insulin and glucagon reserves in ten week-old transplants were not significantly different between recipients that were either diabetic (streptozotocin-treated) or nondiabetic at the time of transplantation. Thus, the initial glucose levels in the host environment, whether elevated or not, did not differentially effect the level of hormones eventually accumulated in transplants.