This paper describes the effect of the amino acid mixture Freamine II on the physical stability of Intralipid fat emulsion. The amino acid-fat emulsion mixture was also administered to patients requiring intravenous nutrition and its clinical and biochemical effects were assessed. The amino acid-fat emulsion mixture was stable on storage for 48 hours as judged by flocculation and particle growth measurements made in the presence of 20 mmol/1 monovalent cations at 2 mmol/1 diavalent cations. Long-term storage of mixtures containing Freamine II is not recommended because of an interaction between the emulsifier and the amino acids. In a small open trial patients maintained their serum albumin concentrations. There was no evidence of impaired pulmonary function even in those subjects with impaired fat clearance.