A hitherto unrecognized entity manifested by complete absence of gamma globulin with otherwise normal serum proteins and recurrent pneumococcal sepsis is described 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. He was unable to produce antibody for the pneumococcus with the four antigenic substances used; a positive Schick test persisted in spite of numerous attempts to reverse it with diphtheria toxoid. No antibody could be demonstrated following administration of typhoid vaccine in the usual manner and his serum was negative for complement-fixing antibodies of epidemic parotitis after he experienced a typical clinical picture of that disease. 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 (3.2 gm. gamma 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 10 different episodes. It is postulated 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. A complete defect of plasma proteins cannot be excluded.