This explorative study was performed to assess basic data on the Mo metabolism of premature infants. Premature (n = 18, gestational age < or = 32 wk, birth weight < or = 1,500 g) and healthy formula-fed term infants (n = 14) were nourished and corrected for gestational age, identically. Plasma was collected at 3, 16, and 52 wk and 72 h balances were performed at 3 wk of age. In the premature infants, these investigations were preceded by two balance studies and an initial plasma collection. Increased Mo intake and low relative urinary excretion resulted in a retention of 4.4 (0.99-7.77) microg Mo/kg initially in premature infants (median, range). Parallel plasma concentrations were 5.5 (2.5-7.3) microg Mo/L, declining to 2.36 (0.73-3.87) microg Mo/L at 4 wk. Term infants rendered 1.49 (0.29-1.7) microg Mo/L (p < 0.05), with no significant differences later. It was concluded that the supplementation of formulas for premature infants with Mo should be recinded until there is evidence for its necessity. Index Entries: Mo; premature infants; trace elements; formula; nutrition.