Protein resynthesis catalyzed by alpha-chymotrypsin was studied to modify the nutritive quality and physical properties of albumin. The increase in substrate concentration produced an increase in enzyme synthetic action. At low substrate concentration, several water activity depressing additives (salts or polyols) in the reaction media enhanced plastein synthesis. Polyols enhanced the synthetic reaction proportionally to an increase in their molecular size. The positive effect of alkali halides was related to an increase in cation size and decrease in anion size. All plastein products showed a clear increase in nutritional value with respect to the substrate.