In 32 beagles heterotopic renal allotransplantations and bilateral nephrectomies were carried out. Control animals (5 dogs) survived 9.4 +/- 1.6 days. 22 recipients were pretreated with donor-specific semisoluble spleen antigen; 5 recipients pretreated with the antigen alone (780 mg/kg body weight) survived 16.6 +/- 2.3 days. A pretreatment with antigen combined with 5 mg/kg body weight Prednisolone resulted in no significant prolongation of survival time (5 animals), but 5 dogs survived significantly longer after pretreatment with the antigen and 50 mg/kg body weight Prednisolone (27.4 +/- 2,7 days). In 5 recipients after preoperative application of 3 doses Prednisolone alone (50 mg/kg body weight each) no prolongation of survival time could be observed (10.2 +/- 0.7 days). We found no correlation between lymphocytotoxic antibody titre and survival time.