Our primary objective in this study was to determine whether transplanted pancreatic islet B cells display normal glucose-stimulated insulin secretory responses. Since transplanted islets are deinnervated and are located in a potentially unfavorable hormonal environment, it is possible that transplanted islets can maintain blood glucose levels but still not be completely normal. Since immune mechanisms may alter secretory responses but fail to cause overt islet necrosis (rejection), we used the BB/W spontaneously diabetic rat as the recipient in these studies. Islets harvested from inbred Lewis rats were transplanted beneath the renal capsule with minimal ALS immunosuppression posttransplantation. The transplanted animals showed a normal response to a glucose tolerance test. After 1 22-155 days of normoglycemia, the islets were retrieved and subjected to 2.8 and 16.7 mM glucose. The results indicate that the islet allografts maintain their secretory response to glucose when compared to donor Lewis islets acutely isolated from the pancreas. Furthermore, the transplanted islets maintained their morphologic integrity. © 1989 by The Williams and Wilkins Co.