Two new erythrocyte pyruvate kinase (PK) variants with severe nonspherocytic hemolytic anemia are presented. These cases are both considered to be homozygous because of the consanguineous marriages in their parents. Their erythrocyte PK's were characterized by the recommended methods of the International Committee for Standardization in Haematology (ICSH). These two variants have been named PK Sendai and PK Shinshu. PK Sendai showed a high K0.5S (phosphoenolpyruvate), was remarkably inhibited by ATP, and was thermolabile, while PK Shinshu demonstrated remarkably low enzyme activity and required a high level of fructose 1,6-diphosphate for activation.