Data on serum immunoreactive insulin (IRI), glucose tolerance, serum growth hormone (HGH), and amino acid levels obtained during previous studies of 35 children suffering from protein-calorie malnutrition (PCM) have been reviewed. In all children intravenous glucose tolerance tests (1 g/kg glucose) were performed after 24 hr of carbohydrate feeding and before protein was introduced into the diets. In 19 of the 35 cases the tests were repeated 24—72 hr after either an albumin or amino acid infusion or milk feeding, and in 29 after 3—6 weeks of refeeding. It was found that the IRI response to glucose paralleled the severity of malnutrition, being low on admission, and improving with recovery. There was a correlation between peak IRI response and both serum albumin and serum alanine levels on admission, but acutely induced increase of albumin and infusions of alanine containing amino acids during therapy did not result in a consistent improvement of insulin secretion. Correlation between peak IRI and the branch chain amino acids barely reached significance on admission. There did not appear to be a direct relation between IRI peak or area and either basal HGH levels or the degree of HGH suppressibility. The glucose intolerance appeared to be related to the poor insulin response, although there were numerous exceptions which indicated that factors other than those recorded in this study are likely to be involved in the production of the glucose intolerance of PCM. The impaired insulin response to glucose characteristic of PCM is associated with severe protein depletion. It is unlikely that the insulin deficiency or the glucose intolerance are related to a single abnormality; they are more likely part of widespread metabolic disturbance or adaptation which varies in importance in each individual. © 1975 International Pediatric Research Foundation, Inc.