Plasma zinc levels in premature infants receiving parenteral nutrition without supplementation of trace elements were evaluated. The mean +/- SE for plasma zinc concentration prior to the start of parenteral nutrition was 53 +/- 6 microgram/dl. During the first two weeks of parenteral nutrition the levels remained low, but did not change significantly. However, from day 14 through day 32 there was a statistically significant (P less than 0.05), progressive decline in plasma zinc values. Perhaps the shortened gestational periods were etiologic in producing the initial low plasma zinc concentration in these patients. Since low-birth-weight infants apparently have a high requirement for zinc, the reduced growth rates of these patients may be related to their apparent zinc deficiencies.