Intestinal mucosa showing environmental enteropathy. (a) Biopsy of the distal duodenum of a 36-month old Brazilian child with environmental enteropathy. Moderate villous atrophy is seen with blunted, flat villi and enterocytes that seem somewhat cuboidal rather than columnar. Elongated crypts can be seen, which result in an abnormal crypt to villus ratio. Most prominent is the striking increase in the number of lymphocytes and plasmacytes present in the lamina propria. (b) Biopsy of the distal duodenum of another Brazilian pre-school age child with environmental enteropathy. The changes are as described for (a) but the villous blunting and hypercellularity within the lamina propria are even more prominent. Photomicrographs kindly provided by Ulysses Fagundes Neto, Universidade Federal de São Paulo.