* This investigation was supported in part by USPHS fellowship 1-F3-AM 7959-02, by USPHS grants AM-07752-02 and AM 09381-01, all from the National Institute of Arthritis and Diseases, and in part by the Medical Research and Development Command, Office of the Surgeon General, Department of the Army, under contract IA-49-193-MD 2413 with the University of Chicago. t Recipient of USPHS Career Development Award l-K3-AM-7959-01. I Beet, E. A., Sickle cell disease in the Balovale District of Northern Rhodesia, E. African Med. J., 23, 75 (1946). 2 Brain, P., Sickle cell anaemia in Africa, Brit. Med. J., 2, 880 (1952). 3 Mackey, J. P., and F. Vivarelli, Sickle-cell anaemia, Brit. Med. J., 1, 276 (1954). 4 Allison, A. C., Protection afforded by sickle cell trait against subtertian malarial infection, Brit. Med. J., 1, 290 (1954). 5 Motulsky, A. G., Metabolic polymorphisms and the role of infectious diseases in human evolution, Human Biol., 32, 28 (1960). 6 Siniscalco, M., L. Bernini, B. Latte, and A. G. Motulsky, Favism and thalassemia in Sardinia and their relationship to malaria, Nature, 190, 1179 (1961). 7 Allison, A. C., and D. F. Clyde, Malaria in African children with deficient glucose-6-phosphate dehydrogenase in Brit. Med. J., 1, 1346 (1961). 8 Neel, J. V., The geography of hemoglobinopathies, in Proceedings of the Conference on Genetic Polymorphisms and Geographic Variations in Disease, ed. B. S. Blumberg (New York: Grune & Stratton, 1961), pp. 102-122. 9 Brewer, G. J., unpublished observations. 10 Neel, J. V., Discussion, in Methodology in Human Genetics, ed. W. J. Burdette (San Francisco: Holden-Day, Inc., 1962), pp. 198-199. 1 Powell, R. D., and G. J. Brewer, Glucose-6-phosphate dehydrogenase deficiency and falciparum malaria, Am. J. Trop. Med. Hyg., 14, 358 (1965). 12 Kornberg, A., Reversible enzymatic synthesis of diphosphopyridine nucleotide and inorganic pyrophosphate, J. Biol. Chem., 182, 779 (1950). 1 Brewer, G. J., and R. D. Powell, The adenosine triphosphate content of G-6-PD deficient and normal erythrocytes, including studies of a G-6-1D deficient man with elevated erythrocytic ATP, to be published, 14 Gross, R. T., E. A. R. Schroeder, and S. A. Brounstein, Energy metabolism in the erythrocytes of premature infants compared to full term newborn infants and adults, Blood, 21, 755 (1963). 15 Beutler, E., R. J. Dern, and C. L. Flanagan, Effect of the sickling trait on resistance to malaria, Brit. Med. J., 1, 1163 (1955). 16 Allison4 has reported evidence suggesting a decreased susceptibility to malaria infections in partially immune individuals with sickle cell trait contrasted with partially immune control individuals.