Hb Presbyterian is a variant hemoglobin that carries Lys at Asn-108 of beta-globin. This variant Lys(beta108) residue enhances the stability of Hb in the deoxy-state, conferring the low affinity for oxygen-binding in vitro, In the present study, we generated mutant mice carrying the Presbyterian mutation (Asn(beta108) --> Lys) at the beta-globin locus by a targeted knock-in strategy, Heterozygous mice showed the expression of Hb Presbyterian in 27.7% of total peripheral blood without any hematological abnormalities, which well mimicked human cases. On the other hand, homozygous mice exclusively expressed Hb Presbyterian in 100% of peripheral blood associated with hemolytic anemia, Heinz body formation, and splenomegaly. Hb Presbyterian showed instability in an in vitro precipitation assay. Erythrocytes from homozygous mice showed a shortened life span when transfused into wild-type mice, confirming that the knocked-in mutation of Lys(beta108) caused hemolysis in homozygous mice. This is the first report on the hemolytic anemia of unstable hemoglobin in an animal model. These results confirm the notion that the higher ratio of an unstable variant beta-globin chain in erythrocytes triggers the pathological precipitation and induces hemolysis in abnormal hemoglobinopathies. (C) 2002 Elsevier Science (USA). All rights reserved.