The authors considered the possibility, for purposes of total parenteral nutrition, to use lyophilized amino-acids as an alternative to the traditional amino-acid solutions, and resolved to check their nutritional and metabolic effectiveness. For this purpose, they appraised some parameters concerning the proteic metabolism in two homogeneous groups of surgical patients, subjected to T.P.N., one with crystallized amino-acids in solution and the other with lyophilized amino-acids. The supply in glucides and in lipides was identic in both groups. It appears evident from the results that the lyophilized amino-acids not only show the advantage of being administrable in nutritional mixtures with reduced volume, but also represent a valid plastic source, and can surely replace the traditional commercial amino-acid solutions.