To determine the adequacy of zinc and copper supplementation for infants receiving total parenteral nutrition (TPN), we performed 24-h balance studies in infants with diarrhea and infants who had recently undergone surgery. Measurements were made at base line, 1, and 2 wk. Mean serum Zn and Cu levels of the diarrhea group remained normal and were low in the postoperative group but normalized over the study period. Mean 24-h Zn and Cu balances were positive in infants with diarrhea and negative in postoperative infants. The high Zn and Cu content in the gastrointestinal fluid loss associated with surgery may have accounted in part for this finding. Normal serum levels of Zn and Cu did not guarantee positive balance. No significant changes were found in serum albumin, alkaline phosphatase, or ceruloplasmin. The current Zn and Cu recommendations may be appropriate only for hospitalized infants who have no excessive gastrointestinal fluid losses.