Preterm infants with birth weights between 1,001 and 1,600 gm were randomly assigned at one week of age to three groups and fed a standard milk-based formula, the same formula with iron, or a soy-based formula with iron. Hematologic values and selenium status were then studied prospectively for five weeks. Rates of decline in hematocrit and hemoglobin did not differ significantly among the three groups and did not correlate with red cell selenium values or glutathione peroxidase activity. Attainment of vitamin E sufficiency was variable among the infants, with no significant intergroup differences. Plasma selenium concentrations did not change significantly, but plasma glutathione peroxidase activity declined consistently in all three groups. Under the conditions of this study, iron at a concentration of 12 mg/L of infant formula did not accelerate hemolysis; nor was there evidence of a direct association between selenium values and early anemia of prematurity.