Present knowledge of trace element nutritional requirements and the effects of TPN solutions unsupplemented with zinc indicate that zinc supplementation must be considered for any patient receiving prolonged TPN. Zinc sulfate appears to be the supplement of choice, and infusions of freeze-dried plasma appear to be an unsatisfactory method for supplying zinc, even during short-term therapy. As long as accepted dosage regimens are followed, there appears to be little risk of toxicity when TPN solutions are supplemented with zinc.