"Inborn Errors of Metabolism" presents the physician with a concise, easily understood, and practical approach to the problem of diagnosis of hereditary disease. Metabolic errors are discussed in the framework of five major divisions: (1) Disturbances in molecular structure—the hemoglobin variants are the major members of this group at the present time. (2) Disturbances in molecular synthesis comprise the deficiencies in formation of macromolecules of plasma proteins and clotting factors. Analbuminemia would probably belong in this group. (3) Disturbances in molecular function is the largest division. It comprises the "metabolic blocks" and may be visualized as a failure of function of the respective enzymes. (4) Disturbances in renal transport mechanisms combines in one division enzymatic defects of a single organ. (5) This section is a category of disease of unknown etiology including disturbances in lipid metabolism and the muscular dystrophies. An appendix of diagnostic methods, many tested in the author's