The effects of a synthetically obtained mixture of amino acids (FACE) were investigated on the trophic and neurosecretory activity of in vitro cultures of fetal rat neuronal cells. The addition of 10(-6) M FACE to the culture medium significantly increased cell DNA content. Secretions of IR-SRIF, IR-VIP, and IR-GRF were also augmented in different proportions by the presence of FACE. Time studies demonstrated that IR-SRIF was significantly increased after 48 (P less than 0.05) and 72 (P less than 0.01) hr of exposure to FACE, and IR-VIP secretion was potentiated after only 24 hr of culture. Dose-response experiments with 10(-7) to 10(-4) M FACE indicated that concentrations of 10(-5) and 10(-4) M significantly increased both somatostatin released to the medium and cell content of IR-SRIF. FACE concentrations as low as 10(-10) M augmented the secretion of IR-GRF, and there was a dose-response correlation between 10(-10) and 10(-5) M FACE. The release and cell content of IR-VIP were also increased by FACE, with a dose-response relation at concentrations of 10(-9) to 10(-6) M. It can thus be concluded that FACE has a powerful effect on the multiplication and survival of fetal cerebrocortical cells and is also an important potentiator of IR-SRIF, IR-VIP, and IR-GRF secretion.