Adrenal medullary tissue from Wistar-Furth rats was transplanted beneath the renal capsule of Lewis rats to determine the effect of in vitro culture of the donor graft and temporary recipient immunosuppression with Cyclosporine A (CsA) on allograft survival. The adrenal medulla was transplanted immediately after dissection or after 1 week of culture, either at 24°C or in the presence of 95% O2 at 37°C. The results showed that neither cultural pretreatments affect the survival of the isografts as indicated by morphologic integrity of the grafts 30 days after transplantation. In the absence of in vitro culture of the donor medulla and short-term CsA recipient treatment, all the allografts were completely rejected at 30 days. Cultural pretreatment of the grafts either at 24°C or in the presence of 95% O2, in conjunction with temporary CsA treatment of the recipient, or CsA treatment alone produced histologic survival of the grafts 30 days after transplantation. Varying degrees of lymphocytic infiltration were present in the grafts. When adrenal cortex was transplanted in conjunction with medullary tissue a bimodal immune reaction was observed; medullary tissue was infiltrated by lymphocytes, while the adrenal cortex remained morphologically intact with no infiltration at all. The experiments performed did not show a benefit in prolonging medulla allograft survival using pretransplant culture of the tissue.