Objective: To assess the impact of a daily oral iron supplementation on hematological status, cell-mediated immunity and susceptibility to infections in children living in an environment where iron de®ciency, malaria and other infections are frequent. Design: Randomized, double-blind iron supplementation including a placebo group. Setting: A village in Togo, West Africa. Subjects: Of the 229 6 ± 36-month-old children of both sexes recruited, 197 with hemoglobin concentration ! 80 gal were included and 163 completed the study. Intervention: Children received daily a placebo (n 79) or a dose of 2 ± 3 mg of elemental iron per kg of body weight (n 84) for 3 months. Hematological, nutritional and immune status were assessed at the beginning and at the end of the supplementation period, and 6 months later. Morbidity was recorded throughout the study. Results: Iron supplementation had a signi®cant and positive effect on iron status of children and no impact on the incidence of infections, especially malaria. Its probable effect on immune status was masked by interference of infections and their treatment, which contributed to improve hematological and immune status in both groups. Conclusion: According to the negative consequences of anemia and iron de®ciency on global child development, control of iron de®ciency by oral iron supplementation in young children has to be conducted, associated with prophylaxis and treatment of malaria and repeated deworming.