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Background: The optimal form and dose of selenium supplementation required to achieve indicators of selenium status equivalent to those in breastfed infants are unclear. Objective: The objective was to evaluate the effect of fortifying infant formula (6 [micro]g Se/L) with 2 concentrations of selenate (7 and 15 [micro]g/L) on biochemical indicators of selenium status and growth at 16 wk in term infants. Design: A randomized dose-response trial was conducted in 3 groups of term infants fed formula with different selenium concentrations [6 [micro]g/L, F + 0 (control); 13 [micro]g/L, F + 7; and 21 [micro]g/L, F + 15] and in a parallel breastfed reference group (BF; 11 [+ or -] 2 [micro]g Se/L). Results: One hundred sixty-one (47% males) infants completed the 16-wk study. Baseline plasma selenium was 0.3 [+ or -] 0.1 [micro]mol/L. At 16 wk, plasma selenium had increased in all groups (P < 0.001) and was greater (P < 0.01) in the F + 7 and F + 15 groups and lower (P < 0.05) in the F + 0 group than in the BF group. Plasma glutathione peroxidase increased in the F + 15 group, decreased in the F + 0 group, and, at 16 wk, was lower in the F + 0 group than in the other groups (all P < 0.05). Erythrocyte selenium and glutathione peroxidase decreased in all groups (P < 0.05), but the magnitude of the change was greater in the F + 0 than in the F + 15 group (P < 0.05). There was no effect of selenium supplementation on growth. Conclusions: Selenate fortification of formula resulted in an increase in plasma indicators of selenium status relative to indicators observed in infants fed low-selenium-containing formula. Although the erythrocyte indicators decreased in all groups, the 21-[micro]g/L dose (F + 15 group) resulted in a smaller decrease and in higher erythrocyte selenium than did the standard formula. Supplementation of low-selenium formula to provide a net selenium concentration close to that found in the breast milk of US women (18 [micro]g/L) may be justified.