Nonarterialized orthotopic liver transplantation with no immunosuppression was performed in 13 mouse-strain combinations. Two strain combinations with major histocompatibility complex class I and class II and minor histocompatibility complex disparity had 20% and 33% survival of more than 100 days, but the other 11 combinations, including four that were fully allogeneic and all with only class I, class II or minor disparities, yielded 45% to 100% survival of more than 100 days. Long-living recipients permanently accepted donor-strain heterotopic hearts transplanted on the same day or donor-strain skin 3 mo after liver transplantation, in spite of detectable antidonor in vitro activity with mixed lymphocyte reaction and cellmediated lymphocytotoxicity testing (split tolerance). In further donor-specific experiments, liver grafts were not rejected by presensitized major histocompatibility complex class I-disparate recipients and they protected donor-strain skin grafts from second set (or any) rejection. Less frequently, liver transplantation rescued rejecting skin grafts placed 1 wk earlier in major histocompatibility complex class I, class II and minor histocompatibility complex, class II or minor histocompatibility complex-disparate strain combinations. Donor-derived leukocyte migration to the central lymphoid organs occurred within 1 to 2 hr after liver transplantation in all animals examined, persisted in the surviving animals until they were killed (>375 days), and was demonstrated with double-immunolabeling to be multilineage. The relation of these findings to so-called hepatic tolerogenicity and to tolerance in general is discussed. (HEPATOLOGY 1994;19:916–924.)