Phosphoglycerate kinase deficiency is a rate, X-linked disorder associated with a severe haemolytic anaemia. In general the deficiency has been demonstrated only in erythrocytes and leucocytes. However, in a subject with this condition, the activity of phosphoglycerate kinase in lymphocytes and platelets was also shown to be less than 5% of the normal value. Following the death of this subject in 1979, the deficiency was also found to occur in tissue samples of brain, skeletal muscle, liver and cardiac muscle, obtained at the autopsy. Values for phosphoglycerate kinase were of the order of 0.5-5% of normal controls. Other glycolytic enzymes which were tested were hexokinase, pyruvate kinase, enolase and 2-phosphoglyceromutase. In general, values for these enzymes were either normal or slightly raised.