The concentration of glucose-6-phosphate dehydrogenase (G-6-PD) was found to be 150-350 units per billion platelets in 52 normal individuals. In 21 of 27 patients with thrombocytopenia the enzyme was found in normal concentrations.

Of the six cases showing thrombocytopenia with lowered enzyme concentration, five were examples of acute leukemia and one of disseminated lupus erythematosus.

In three individuals with "primaquine sensitive" erythrocytes the defect in the platelet G-6-PD was also present.

The significance of the lowered enzyme activity in the six patients with thrombocytopenia is not known.

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