A study has been made regarding three boys who had agammaglobulinemia and who were seen at the Mayo Clinic during a period of seven months. In each there was a history of frequent infections since infancy. All three patients demonstrated relatively normal serum proteins except for greatly decreased amounts of gamma globulin. The deficiency in gamma globulin was demonstrated by use of paper electrophoretic analysis of serum proteins. One of the patients, an infant, died while under treatment at the clinic. The second patient continued to have frequent infections in spite of the administration of gamma globulin at frequent intervals; he died later at home. The third patient has been maintained in good health by monthly injection of gamma globulin.