Among 27 patients who received minor ABO-incompatible partial liver transplantations and 19 who received major ABO-incompatible partial liver transplantations from living donors, 2 developed hemolytic anemia within 2 weeks after transplantation. These 2 patients had received livers from their living fathers whose blood type was ABO-incompatible. B-to-A transplantation was performed in patient 1 and O-to-B transplantation was performed in patient 2. Anti-A IgM and IgG were detected in the serum of patient 1, and anti-B IgM and IgG were detected in the serum of patient 2. These antibodies were eluted from the red blood cells of the patients. The coexistence of donor-specific DNA in the peripheral blood of the patients proved that they had chimerism, and graft-versus-host antibody production due to passenger B lymphocytes in the donor's liver was subsequently confirmed.