Trace element deficiencies in patients receiving total parenteral nutrition (TPN) have been observed with increasing frequency. Zinc deficiency is a well-recognized complication in TPN and has been variously attributed to the low zinc content of the TPN diet [13, 22, 271, the increased zinc requirements of anabolism [14], and the associated clinical conditioning factors predisposing to a lowered zinc status [21], such as the increased fecal zinc losses of inflammatory bowel disease or the increased urinary zinc losses of catabolism. The urinary zinc losses during intravenous infusion of amino acids in TPN have been reported by different investigators to be low [3, 8, 141, normal [22], and excessive [9, 12, 141. These conflicting observations and the relative importance of zincuria in TPN require clarification. Zincuria and aminoaciduria are associated in some patients receiving TPN [24], and the ingestion of certain amino acids produces an increased zincuria [6, 11, 15, 161. Amino acids form complexes with zinc [18], and it has been suggested that zinc chelation by some amino acids facilitates the ultrafiltration in the kidney and subsequent urinary excretion of zinc [19]. The distribution and the total quantity of each of the amino acids infused during TPN vary with the type of amino acid preparation. It is probable that the pattern of zinc complex formation varies in the different amino acid preparations. Consequently zincuria may vary quantitatively and qualitatively with the administration of the different amino acid preparations. Amino acid-zinc chelation in these solutions and in the corresponding urine has not been previously demonstrated. Clinical zinc deficiency in adults receiving TPN has been reported more frequently in association with specific amino acid preparations [ 14, 25, 271. Excessive zincuria has also been reported with a particular TPN preparation [12, 14, 241. Identification of those factors in amino acid preparations which predispose to zinc deficiency, as well as excessive zincuria, should encourage necessary modifications and result in a reduction in the incidence of this complication of TPN. This study compares the zincuria and aminoaciduria following a short infusion of different commercially available amino acid preparations and demonstrates the chelation of zinc in these solutions and in the corresponding urines.