 Patients in the study who were immunodeficient and adenosine deaminase deficient were found to have over 50 times the levels of dATP in their erythrocytes compared to non-immunodeficient, adenosine deaminase deficient patients.This is abnormal and provides evidence that increased erythrocyte dATP levels are the toxic metabolites responsible for immune system deficiency in individuals with adenosine deaminase deficiency.Infusion of normal, non-enzyme deficient erythrocytes resulted in the loss of dATP in the erythrocytes of these individuals.