Healthy term infants were given a low-fat powdered milk fortified with 15 mg/100g of iron, as ferrous sulphate, for one year, starting at three months of age. The control group received non-fortified milk. A total of 510 infants entered the study, and 314 could be studied at the age of 15 months. Consumption of the fortified formulas was monitored through iron determinations in stools. Groups had a comparable hemoglobin concentration at the age of three months. Hemoglobin was higher in the fortified group at nine months (11.7 +/- 1.0 vs 11.4 +/- 1.1 g/dl, p less than 0.02), and 15 months (12.0 +/- 1.1 vs 11.4 +/- 1.2, p less than 0.001). The percentage of subjects with anemia (Hb less than 11.0 g/dl) was lower in the fortified group: 14.8% vs 27.7% of the controls at nine months and 7.0% vs 35.3% at 15 months. Percentages of subjects with iron deficiency (Fe/TIBC less than 9%) were lower in the fortified group: 28.0% vs 49.1% of the controls at nine months, and 20.0% vs 41.8% at 15 months. Although the fortified milk markedly improved iron nutrition, deficiency of this mineral was still high in the group receiving it. This was probably due to the low bioavailability of iron when administered with non-modified milks.