Two factors which have gained attention as possible contributors to success of renal allografts are freedom from infection with cytomegalovirus (CMV) after transplant and administration of multiple blood transfusions pretransplant. In order to determine the interrelationship of these two variables, we analyzed 55 recipients of well matched (at least two antigens) cadaveric kidneys. In this study, absence of CMV infection and receipt of multiple transfusions both provided favorable outcomes. When patients were grouped by both factors, those who were free of infection and received multiple transfusions did significantly better than any other combination. Infection with CMV decreased the frequency of allograft survival in multiply transfused patients to a point intermediate between the above group and those who had not been multiply transfused. Since CMV infection can be predicted by measurements made pretransplant, and since up to one-quarter of CMV infection which develops post-transplant is transmitted with the allograft, administration of multiple transfusion to all patients and the use of donors who are free of latent CMV infection for CMV antibody-negative potential recipients should increase allograft success. For those potential recipients who already have latent CMV infection, further study will be necessary to determine what stimuli can be given pretransplant to prevent the interference with the beneficial effect of multiple transfusion.