Reversible haemolytic anaemia associated with decreased red cell half-life and 
reticulocytosis was studied in 10 patients with Zieve's syndrome. Since the 
underlying cause of the red cell destruction is as yet unknown, we determined 
the critical metabolic functions of the red cells in order to define the assumed 
intracorpuscular defect causing haemolysis. The glucose metabolizing enzymes had 
normal or raised values. - In view of the diminished ATP and raised 
2,3-diphosphoglycerate (2.3 DPG) levels - a combination which suggests a 
pyruvate kinase (PK) deficiency - additional procedures were carried out in 
order to detect an abnormal activity of the red cell PK. Studies of biochemical 
properties of PK such as thermostability, Michaelis-Menten constants, and 
activation and inhibition tests brought results markedly deviating from the 
norm.-Fractions containing old cells particularly disclosed PK instability. A 
defective red cell matabolism resulted which was measurable through 
ATP-instability, altered glucose utilization and lactate production. - 
Experimental cell aging procedures led to a markedly decreased red cell 
metabolism. These assays revealed that mutations of PK-control mechanisms might 
be involved as factor triggering haemolytic anaemia of Zieve's syndrome.