The concentrations of 11 amino acids were determined in 9 regions of the rat brain following the acute administration of the antidepressant drugs imipramine and Org. GB94, and chlorpromazine. The amino acids were determined as their dansyl derivatives. Unequivocal changes were only found in the concentrations of gamma-aminobutyric acid, alanine, asparagine + glutamine, glycine and taurine in some brain regions. Chlorpromazine produced the greatest change in these amino acids. Imipramine and Org. GB94 had qualitatively different effects on the concentrations of the amino acids in the 9 brain regions.