Thirty eight children with a haemoglobin concentration of 106-110 g/l were given either oral iron (n = 17) or placebo (n = 21) for two months. The treated group achieved a significantly higher rise in haemoglobin concentration; in a quarter it was greater than 20 g/l. While those with the lower mean corpuscular volume and ferritin showed greater rises in haemoglobin these indices were of little value in predicting response in an individual child.