• More than 70 case reports have defined congenital agammaglobulinemia and acquired hypogammaglobulinemia as disease entities. These patients present with repeated, severe bacterial infections. They lack normal isohemagglutinins, anti-A and anti-B, and are unable to form antibodies. Serum electrophoretic studies reveal a striking absence of gamma globulin. Definite diagnosis is best made by quantitating gamma globulin immunochemically. Reports indicate that the immunochemically determined concentration of gamma globulin is 0 to 30 mg. per 100 cc. in congenital cases, 0 to 76 mg. in acquired cases, and approximately 1,100 to 2,100 mg. in normal persons. Important considerations in treatment are the prompt control of any existing infection with antibiotics and the prevention of recurrences with maintenance gamma globulin therapy. One of the patients here reported on appeared to have acquired hypogammaglobulinemia, except that his level of circulating gamma globulin (200 mg. per 100 cc.) was above that generally accepted for this diagnosis. A second patient developed repeated infections after a diagnosis of multiple myeloma. His serum contained large amounts of gamma myeloma protein, and antigen injections produced only partial responses. In both cases it was decided to withhold gamma globulin therapy because of uncertainties in the diagnosis. Gamma globulin therapy is painful, expensive, and must be given indefinitely. The authors urge that it not be undertaken without firm proof of the diagnosis.