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 deficiency, malaria and other infections are frequent. METHODS Randomized, double-blind iron supplementation including a placebo group. METHODS A village in Togo, West Africa. METHODS Of the 229 6-36-month-old children of both sexes recruited, 197 with hemoglobin concentration >/=80 g/l were included and 163 completed the study. METHODS 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 significant 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. CONCLUSIONS According to the negative consequences of anemia and iron deficiency on global child development, control of iron deficiency by oral iron supplementation in young children has to be conducted, associated with prophylaxis and treatment of malaria and repeated deworming. BACKGROUND Program supported by IRD. European Journal of Clinical Nutrition (2000) 54, 29-35