Forty two children were admitted to this hospital between 1975 and 1980 with severe iron deficiency anaemia and 8 of them also had oedema caused by a low concentration of serum proteins. These 8 patients, aged 8-24 months, and 13 age matched controls were investigated. The patients had excessive faecal loss of 59FeCl or 51Cr-albumin, or both; their jejunal biopsy specimens showed little decrease in the ratio of villous height to crypt depth; and they had fewer intraepithelial lymphocytes and cells containing IgA than controls. They were all treated with an oral ferrous iron preparation and the oedema, hypoproteinaemia, and low haemoglobin concentrations rapidly resolved. These results show that immunologically mediated hypersensitivity is not implicated in iron deficiency anaemia associated with hypoproteinaemia.