It remains uncertain whether xenotransplantation can sensitize the recipient to alloantigens, rendering subsequent allotransplantation unsuccessful. This is of considerable importance if a xenograft is to be used as a “bridge” to support the patient until a suitable allograft becomes available. When sera from 9 baboons that had received pig or African green monkey heart or liver xenografts were tested against a panel of lymphocytes from 5 or 6 potential donor baboons, positiv ity was seen in only 1 baboon (and then to only 2 of the potential 5 donors). In 4 baboons that had undergone previous xenotransplants (1 from this series of 9 baboons and 3 others), subsequent organ allografting was not followed by hyperacute, antibody-mediated, or accelerated cellular rejection. We conclude that organ xenotransplantation using discordant or concordant donor species does not prohibit subsequent allo-transplantation. © 1995 by Williams & Wilkins.