The stability of total nutrient admixture (TNA) systems containing a soybean oil emulsion (Soyacal) has been reported with only one amino acid (AA) solution. This study was conducted to compare the physical stability of 10 TNA systems varied only by the AA solution used. All systems contained electrolytes, vitamins, trace elements, and heparin. The volume ratios of AA, dextrose 70% and lipid emulsion 20% were 1:1:1. Solutions were stored at 4 degrees C for 14 days and then held at ambient temperature for an additional 4 days. Each TNA was serially analyzed on days 0, 1, 3, 5, 7, 14, 15, 16, 17, and 18 for gross visual appearance, pH, osmolality, mean particle diameter, and particle size distribution. The AA solutions evaluated include: Travasol 8.5% and 10%; Aminosyn 8.5% and 10%, Aminosyn RF 5.2%; FreAmine III 8.5% and 10%; FreAmine HBC 6.9%; HepatAmine 8.0%; and NephrAmine 5.4%. The pH values of the Aminosyn solutions were lower than those of other products; however, the pH values of all TNA systems were greater than 5.7, which supported particle stability. The osmolality was not affected by the AA solutions. Based upon particle size distribution, 95% of all particles were less than 0.608 micron in diameter, with means ranging from 0.286 micron to 0.309 micron. The largest particle observed by light microscopy was 6.9 micron. These data indicate that TNA systems prepared with the 10 AA solutions and Soyacal 20% are physically stable.