The pattern of intracellular aminoacids may be reproduced individually and is different for each illness. This study seeks to measure alterations in this pattern in rats after the administration of hypocaloric peripheral parenteral nutrition (HPPN), group B, for five days, by comparing them with rats subjected to conventional fluidtherapy, group A, for the same period. HPPN tolerance was good in all cases. Our results show a higher tendency to glyconeogenesis in group A, measured by a reduction in the glycogenic aminoacids especially alanine. An increase in branched aminoacids was observed in group A due to an increase in proteolisis. The animals in group B showed a lesser reduction in the intracellular aminoacids necessary for glyconeogenesis, especially glycine. HPPN, was found, to alter the aminoacids pattern in fasting rats. The results might be corroborated in humans studies.