The purpose of this study was to determine whether gamma-aminobutyric acid (GABA) affects the rate of brain protein synthesis in ovariectomized female rats. Experiments were done on two groups of 24-wk-old ovariectomized female rats given 0 or 0.5% GABA added to the 20% casein diet. The concentrations of plasma growth hormone (GH) increased significantly with the 20% casein+0.5% GABA compared with the 20% casein diet alone. In the brain regions, GABA treatment to the basal diet elevated significantly the fractional and absolute rates of protein synthesis. In brain regions, the RNA activity [g protein synthesized/(g RNA x d)] significantly correlated with the fractional rate of protein synthesis. The RNA concentration (mg RNA/g protein) was not related to the fractional rate of protein synthesis. The results suggest that the administration of GABA to ovariectomized female rats is likely to increase the concentrations of plasma GH and the rate of protein synthesis in the brain, and that RNA activity is at least partly related to the fractional rate of brain protein synthesis.