Abstract: Pyruvate kinase deficiency is a blood disease characterized by hemolytic anemia. PCR analysis of cDNA leukocytic extracts of patients with hereditary pyruvate kinase deficiency anemia revealed two overexpressed markers when compared to extracts from healthy individuals. These two markers, proposed as human markers A and B and associated with hereditary hemolytic anemia, have been cloned (HUMDNAMA and HUMDNAMB, Gen Bank Association numbers M64700 and M64701). Our attention has focused on human DNA marker B, a 451 bp open-reading frame. The marker has been cloned in the bacteria vector pGEX-2TK and the expressed protein, called HMF (hemolytic anemia related factor), has been tested for biological activity. It has been observed that the HMF-glutathione transferase fusion protein, added to freshly prepared leukocytes cultures, has an immediate cytotoxic effect and a delayed lymphoblastic effect. The lymphoblastic effect is greatly enhanced when erythrocytes are added to the leucocytes.