The iron status of 49 preterm infants (mean gestational age 33.1 weeks) was assessed serially during the 1st year of life. Haemoglobin concentration, serum ferritin, serum transferrin, serum iron, and transferrin saturation were measured on nine occasions in each infant. In 16 infants of gestational age 28-32 weeks the haemoglobin concentration was significantly lower at 3, 6, and 9 weeks when compared to 33 infants of gestational age 33-36 weeks. For all other measures of iron status there were no significant differences between these gestational age groups. For the entire group of 49 infants the mean haemoglobin concentration reached a nadir of 11.2 g/dl at 9 weeks. Mean serum iron and transferrin saturation reached peaks of 24 mumol/l and 65%, respectively, at 3 weeks. The mean serum ferritin remained over 100 micrograms/l until after 18 weeks. 13 infants (26%) had iron deficiency defined as either serum ferritin less than 10 micrograms/1 (n = 10) or transferrin saturation less than 10% (n = 5) or both (n = 3).