Hypertension secondary to renal transplantation was studied in our experimental model in the rat. In this model an intravenous injection of donor strain blood into recipients of allogeneic donor kidneys prior to transplantation was used to prolong the allograft survival. A reduced renal function associated with the hypertension was suggestive of incomplete prevention of the rejection process. We studied the effect of cyclosporin A, either alone or as adjuvant immunosuppressive therapy, on renal function and systolic blood pressure. Either way, cyclosporin A resulted in normotensive allograft recipients and in a better function of the graft when compared with recipients pretreated with donor strain blood only.