SYNOPSISThe relative importance of growth, composition of the diet, and renal function in maintaining internal stability during the first 2 critical weeks when the newborn baby is endeavouring to adapt to his new environment has been investigated. The technique used was serial daily metabolic balance studies in normal premature babies, in oedematous premature babies, oedematous premature babies with respiratory distress, dysmature babies, infants of diabetic mothers, and full term infants fed pooled human milk.