Publisher Summary The chapter discusses a hitherto unrecognized entity manifested by complete absence of gamma globulin with otherwise normal serum proteins and recurrent pneumococcal sepsis in an 8-year old male. The patient appears to be normal in other respects, and after extensive study no structural or functional change could be demonstrated in any body system, although gamma globulin by electrophoretic analysis of his serum was consistently absent. Gamma globulin could be demonstrated in his serum after concentrated immune human serum globulin was administered subcutaneously, and its gradual disappearance could be followed by electrophoretic analysis over a period of approximately six weeks. Concurrently, and following the administration of human globulin at monthly intervals, he has been free of pneumococcal sepsis for more than a year, whereas he had experienced clinical sepsis at least 19 times in the previous four years in which eight different types of pneumococci had been recovered from blood culture during ten different episodes. The chapter postulates that by some acquired “influence”, the patient's antibody mechanism has been altered so that he is no longer able to synthesize and/or hold antibody to a specific organism.