A new case of phosphoglycerate kinase (PGK) deficiency is described. The propositus displayed episodes of rhabdomyolysis crises and acute renal failure but did not exhibit any sign of hemolysis. A severe deficiency in phosphoglycerate kinase was revealed in muscle and was also found in erythrocytes, white cells and platelets. A partial defect in the same enzyme was present in the mother's and the two daughters' erythrocytes, indicating a X-linked recessive genetic transmission of the enzyme defect. In the propositus, erythrocyte ATP concentration was normal, although 2,3-diphosphoglycerate and triose phosphate levels were moderately increased. Lactate production from glucose, in vitro, was close to normal in intact red cells. The partial PGK was characterized by an increased Km for ADP and more especially for ATP, reduced thermostability, and diminished electrophoretic mobility. Lack of this enzyme, which is a key step in the glycolytic process (generation of one molecule of ATP), is thought to be responsible for rhabdomyolysis, a fact that has not been reported previously.