In these three papers the body build of infants during health and disease is described quantitatively. This is done by comparison of ratios of various external dimensions to the total body length. In the first paper the technique for measuring the external dimensions of the body in infants is described and various sources of error discussed. In the second paper general empirical formulae for the relationship between various external dimensions and total body length in healthy infants are developed. By comparing two groups of infants from different social environments, it is shown that environment may influence body build. In the third paper the results obtained in the second paper for healthy infants are used for comparison with sick infants. Various differences in the body build of infants with acute intestinal intoxication, tetany and eczema are described.