Consecutive deaths of children in Guatemala City were investigated with a view to discovering possible correlations between malnutrition, enteric infection and diarrhoeal disease. Malnutrition and diarrhoeal disease were common in this childhood population. It was found that enteric pathogens did not occur in large enough numbers to constitute a major cause of diarrhoeal disease. Children with malnutrition and diarrhoeal disease not associated with enteric pathogens were noted to have a non-ulcerative inflammatory reaction in the jejunal mucosa. The jejunum of these children contained an abnormally large population of bacteria, not recognized as bacterial pathogens, and whose presence may be the basis of diarrhoeal disease in children suffering from malnutrition.