Asymptomatic small intestinal disease characterized by abnormalities of structure and function has been reported from many developing countries. Abnormalities of structure include changes in villus architecture and in appearance under both the light and the electron microscope. Changes in function include abnormalities in the absorption of xylose, fat, vitamin B(12), amino acids, and dipeptides and excessive faecal losses of nitrogen and energy. The etiology of the condition is unknown but appears to be closely related to exposure to the environment. The nutritional consequences of this condition have not been fully explored but for people living on marginally sufficient dietary intakes they may be extremely important.