G6PD deficiency was discovered in 1956. It causes drug-induced acute hemolysis and is inherited by a sex-linked recessive trait. While the disorder is frequently seen in Negroes and inhabitants around the Mediterranean basin, it is rare in Japanese, the frequency of which is about 0.1%. As to the G6PD genetic variants, about 120 variants have been discribed so far in the world and 10 variants were found in Japan. Pyruvate kinase (PK) deficiency was first discovered in 1961. The disorder is inherited by an autosomal recessive trait and causes chronic hemolytic anemia. 29 cases were found in Japan. Using paremeters such as enzyme activity, substrate affinity, velocity maximum, urea stability as well as electrophoretic mobility, we have been able to differentiate several PK variants. The procedures for the characterization of PK variants have not standardized as yet but there is a treand to do so and hopefully this can be accomplished fairly soon. In both G6PD deficiency and PK deficiency, there is a certain correlation between the characteristics of abnormal enzymes and clinical manifestations.