OBJECTIVE New Zealand soils are deficient in the essential micronutrient, selenium. New Zealand infants have low selenium levels at birth and experience a further decline if fed cows milk based formula. This study examined the selenium status of infants fed with a new commercially available selenium supplemented formula. METHODS Forty-four newborn infants, whose mothers wished to formula feed, were randomized in an open controlled trial to be fed a commercially available selenium supplemented cows milk formula (containing 17 micrograms Se/L) or an unsupplemented formula (containing 4.6 micrograms Se/L). Cord, 1 and 3 month blood samples were obtained for selenium status (plasma and red cell selenium and glutathione peroxidase) and thyroid function. RESULTS Mean plasma selenium and glutathione peroxidase values were significantly higher in supplemented than unsupplemented infants at 1 month (unpaired t-tests; P < 0.0001 and P = 0.001 respectively) and 3 months (P < 0.0001 and P = 0.0005). Analysis within treatment groups between time points (paired t-tests) showed that selenium supplementation prevented the fall in plasma selenium from birth to 1 month seen in unsupplemented infants and was associated with a rise in levels between 1 and 3 months (P = 0.002). CONCLUSIONS Supplementing cows milk formula with selenium to replicate the levels found in breast milk is nutritionally sound. Feeding from a few days of age with a formula containing 17 micrograms Se/L in infants with low selenium status at birth is sufficient to cause a rise to 80% of adult levels at 3 months of age.