Symptomatic zinc deficiency was observed in a 24-week gestation, 640 g birthweight infant fed exclusively with maternal breast milk. Our hypothesis was that subclinical Zn deficiency is not uncommon in very low birthweight infants because fortified human milk and preterm formula may contain little Zn. Zinc serum concentrations determined in 26 consecutive very low birthweight infants (gestational age 23-32, median 27 weeks), prior to discharge, at a chronological age of 37-121 (median 72) d, were found between 1.0 and 14.0 (median 6.4) micromol/l, in 14 infants they were below the normal range of 7.6-15.0 micromol/l. Serum alkaline phosphatase and iron intake did not correlate with Zn concentrations. Nutritional supply of Zn and other trace elements by breast milk fortifiers and infant formulas currently used in Germany does not appear to meet the demands of rapidly growing extremely low birthweight infants during the first months of life.