Since the initial description of agammaglobulinemia in 1952, a large number of patients with a wide variety of primary immune deficiencies have been described. In an attempt to clarify the categorization of these immune disorders, the World Health Organization recently convened a group of investigators who proposed a classification of the primary immunodeficiencies. The complete report of this committee will be published shortly in the Bulletin of the World Health Organization. A portion of the report is quoted below:Immunological responses are classically divided into those mediated by humoral antibody and by cells. Both depend upon the activity of small . . .