The aim of this study was to assess the neurochemical effects produced by short-term dietary soy peptide ingestion in C57BL/6 wild-type mice and in serine-deficient mice that were created as a genetic serine-deficiency disease model. D, L-Amino acid analysis demonstrated that overnight oral ingestion of a 35% (w/v) soy peptide solution significantly increased the hippocampal tissue content of certain neuroactive amino acids in both genotype groups of mice. These amino acids included the neurotransmitter l-glutamate, its precursor L-glutamine, the neuromodulator d-aspartate, and branched-chain amino acids l-valine, l-leucine, and l-isoleucine. Soy peptide ingestion caused similar increases in contents of L-glutamine and branched chain amino acids in the cerebral cortex. Oral ingestion of a 150 mM L-serine solution did not alter contents of these amino acids in the hippocampus and the cerebral cortex in both genotype groups. The present findings indicate that the short-term oral intake of soy peptide positively modulates the levels of certain neuroactive amino acids in the adult brain.