2. Janeway CA, and Gitlin D: Gammaglobulins, Adv Pediatr 9:65, 1957. 3. Willenbockel U: Transitorisch-protahiertes Antik6rpermangelsyndrom bei zweieiigen Zwillingen, Z Kinderheilkd 84:477, 1960. 4. Barandun S: Die Klinik des Antik6rpermangelsyndroms, Helv Med Acta 26:163, 1959. 5. Gleich GJ, Averbeck AK, and Swedlund HA: Measurement o f IgE in normal and allergic serum by radioimmunoassay, J Lab Clin Med 77-690, 1971. 6. Rieger CHL, Lustig JV, Justman RA, and Rothberg RM: Immunologic function of patients with chronic benign lymphadenopathy, Eur J Pediatr 124:51, 1976. 7. Nelson LA, Peri BA, Rieger CHL, Newcomb RW, and Rothberg RM: Immunity to diphtheria in an urban population (in preparation). 8. Yount W J: Imbalances of IgG subclasses and gene defects in patients with primary hypogammaglobulinemia, in Bergsma D, Good RA, Finstad J, and Paul NW, editors: Immunodeficiency in man and animals, Sunderland, Mass. 1975, Sinauer Associates, Inc, pp 99-107. 9. Soothill JF: Immunoglobulins in first-degree relatives of patients with hypogammaglobulinemia, Lancet 1:1001, 1968. 10. Good RA, Kelly WD, R6tstein J, and Varco RL: Immunological deficiency diseases, Prog Allergy 6:187, 1962.