This volume gives positive indication that advances have been made in our knowledge of vitamins and hormones. Data are presented that demonstrate that antibody response can be inhibited in deficiency states. Animal work has shown that the essential fatty acids protect animals against x-irradiation injury, maintain capillary pressure in the subcutaneous vessels, are necessary for normal cholesterol transport and metabolism, and are required for successful pregnancy and lactation. The chapter discussing the biosynthesis of ascorbic acid indicates that new tools are available to study the problem and its relation to other physiological processes. Two chapters discuss the physiology and chemotherapeutic action of vitamin B12. A brief chapter on the vitamin requirements of human beings is included. The conclusion seems to be that vitamins, including vitamin B12, will correct metabolic disorders resulting from existing vitamin deficiencies. There is a fine presentation of the question of parasitic infections and nutrition.