In a longitudinal study from age 3 to 15 mo, 276 term, healthy, spontaneously weaned infants received a full-fat acidified milk fortified with 15 mg of elemental Fe as ferrous sulfate and 100 mg of ascorbic acid/100 g of powder and 278 control infants received milk without additives. At ages 9 and 15 mo significant differences were encountered in all measures of Fe nutriture in favor of the fortified group (p less than 0.001). Anemia (Hg less than 110 g/L) was present in 25.7% of unfortified infants compared with only 2.5% in those fortified at age 15 mo. Saturation of transferrin less than 9% was present in 33.8% and serum ferritin less than 10 micrograms/L in 39.1% of the nonfortified infants. The figures for the fortified group were 7 and 8.5% respectively. The efficiency of the fortified acidified milk in eradicating Fe deficiency in the infants while discouraging use by other family members make this milk a useful targeted product in programs of supplementary food distribution in the underdeveloped world.