Three forms of agammaglobulinemia have been described: (1) the physiologic or transient form in infancy, (2) a congenital inherited form occurring in males, and (3) an acquired form occurring in both sexes and associated with the onset of infections in adolescents or adults. The congenital and acquired forms are due to absence of plasma cells in the tissues; these cells appear to be the sight of synthesis of gamma globulin. Using an immunochemical technique it was demonstrated that at least two plasma proteins besides gamma globulin are absent or markedly diminished in congenital and acquired agammaglobulinemia. These proteins appear to belong to the group of beta globulins. A previous finding was confirmed—that in patients with agammaglobulinemia the deficiency of gamma globulin is often not complete.