Fetal rat pancreases frozen to and stored at −196 C were used for transplantation into streptozotocin-induced diabetic syngeneic adult recipients. Transplantation was carried out either directly after thawing from −196 C, or after a 21-day growth period in a syngeneic, normoglycemic adult carrier. All transplants were placed under the kidney capsule. A single, frozen fetal rudiment was sufficient to restore blood glucose, urine volume, and urine glucose to normal, provided it had first been grown for 21 days in a normal carrier. In vitro perfusion studies showed that fetal pancreases stored at −196 C were equivalent to fresh rudiments in their responses to a glucose stimulus.