The present study investigates whether fetal adrenal transplants into the omentum of adrenalectomized rats will be integrated into the recipient's endocrine system to provide competent adrenocortical function. The results demonstrate that fetal adrenals graft with a rich vascular supply, mature histologically, and produce increasing levels of corticosterone. When bilateral adrenalectomy is performed in the recipient, survival is prolonged and addisonian crisis can be prevented. Moreover, adrenocorticotrophic hormone levels decrease with increasing levels of corticosterone, indicating that the fetal grafts are integrated into the physiological pituitary-adrenocortical feedback system.