Sixty children aged 1-3 years with protein malnutrition were involved in the present study. Measurements were made of plasma transferrin receptor (TfR), haemoglobin (Hb), ferritin, transferrin and Fe in comparison with twenty apparently healthy age- and sex-matched reference children in Nigeria. Plasma TfR was measured by an immunofluorometric assay. The mean plasma concentrations of both albumin (37 g/l) and transferrin (1·88 g/l) were within reference ranges in the ‘healthy’ children. The malnourished children had severe protein deficiency as indicated by their significantly lower mean plasma albumin (24·4-28·2 g/l; P < 0·0001) and transferrin (1·24-1·53 g/l; P < 0·0001) concentrations in comparison with the reference children. In the reference children, the traditional indicators of Fe nutrition (plasma Fe, transferrin Fe saturation and Hb) were within the reference ranges, but ferritin values were raised, indicating acute or chronic infection and/or inflammation. The mean concentrations of plasma TW (4·2-5-2 mg/l) in the malnourished group were significantly lower than the mean (6·1 mgn) of the reference children (P=0·0009). In the children with severe malnutrition, none of the indicators of Fe status except Hb (81·5-86·7 g/l; P<0·0001) showed Fe deficiency, including the serum concentration of TfR and the TfR : ferritin ratio, although the Fe status was lower than in the reference children (for Fe P = 0·009; and ferritin P=0·0004). In the absence of haemodilution, the low Hb values are a clear indication that the malnourished children were Fe deficient; none of the other indices was indicative of Fe deficiency. This is the first report of TfR levels in malnourished and healthy African children.