The compatibility and stability of the following additives in an 8% amino acids and 50% dextrose solution intended for total parenteral nutrition were studied: potassium phosphate, calcium gluconate, magnesium sulfate, multiple vitamine mixtures, folic acid, cyanocobalamin, phytonadione, insulin, ampicillin, cephalothin, kanamycin and gentamicin. In addition to physical examination, techniques of ultraviolet spectroscopy, thin-layer chromatography and microbiologic assay were used to delineate compatibility characteristics. The principle compatibility problems are generated by elevated concentrations of calcium and phosphate. The efficacy of ampicillin, cephalothin and kanamycin in the amino acids/dextrose solution, with or without additives, did not appear to be significantly different from control samples prepared in sterile water. It appeared that gentamicin might be significantly more effective in the test solutions than in sterile water, but further investigation is needed to verify this. A comprehensive study of the stability of vitamins in parenteral nutrient solutions must be made before a final judgment can be made.