A 1.8 ml iron supplementation of ferrous sulfate is administered for 90 days to 76 Mapuche infants, 12 months of age, male and female, from the rural area of the Cautin province of Chile. The iron nutrition is evaluated before and after the supplementation, through: hemoglobin, haematocrit, transferrin saturation and seric ferritin. Stools test are taken at the infant's home, to confirm the supplement intake and to measure the iron excreted. To study the contained of dietary Fe a Recordatory 24 hour Inquest (RI) is applied moreover a Proximal Chemical Analysis (PCHA) to meal test proceeding from the infant's homes. At 12 months before starting the supplementation, the anemia prevalence was of 28.3%, but it disappear as a result of the intervention. Also 65.3% of the infants showed and increase of 1 g or more on their hemoglobin, which indicates that they were anemic at the beginning of the iron supplementation. By means of this therapeutic test it was find 31% more of anemic infants, indicating more sensibility of this method. The high levels of anemia prevalence are due to the low iron intake, characteristic of the non lactious foods, which according results of the RI reaches an average of 2.8 +/- 1.2 mg of Fe/day, versus 4.8 +/- 4.0 mg of Fe/day according to PCHA. The observed difference between both test showed that there is a process of food environmental contamination, by the use of iron utensils and great soil contact. The high environmental contamination could also be proved by the high iron excretion stools (140 mg of Fe/100 g of stools). This method used to measure the Fe excretion of the supplement, would not be valid in rural population groups with similar characteristics to those of the studied group, because it does not discriminate between the intake and the extremely high environmental contamination. To prevent anemia due to iron absence in infants, it is absolutely necessary to have some iron fortified food starting at 6 months of age, as a complement for breast milk.