METHODS The clinical and biochemical aspects of two cases of PK deficiency associated with chronic hemolytic anemia in two unrelated patients are reported. The residual erythrocyte PK enzymes in both patients were characterized by the recommended methods of the International Committee for Standardization in Hematology (ICSH). CONCLUSIONS Patient (W.Q.) had 60% residual PK activity and may be considered homozygous on the basis of consanguinity in the family. This patient suffered from moderate hemolytic anemia that improved after splenectomy. The enzymatic properties were: low activity, moderate thermal stability, reduced affinity for phosphoenol-pyruvate (PEP), and normal electrophoretic mobility. Patient (E.O.) had 42% residual PK activity and may be considered compound heterozygous since his parents are not related. He suffered from moderate hemolytic anemia. The enzymatic properties were: low activity, moderate thermal stability, reduced affinity for PEP and minimal retardation in electrophoretic migration. Theses two cases of PK deficiency are the first to be discovered in Jordan and probably the first in any Arab country.