The effects of strychnine (STRY) on ion channels activated by N-methyl-D-aspartate (NMDA), kainate (KA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolpropionate (AMPA) and quisqualate (QUIS) were studied using Xenopus oocytes, microinjected with mRNA from rats' brains. STRY reduced NMDA-, KA- and AMPA-induced membrane currents in a dose-dependent manner. The effect was more pronounced with NMDA than with KA and AMPA. QUIS-induced membrane currents were not affected by STRY. The depressive effect of STRY on NMDA responses was voltage dependent. The effect of STRY on the NMDA-induced membrane currents remains unchanged when the concentration of NMDA or glycine was increased. Intracellular injection of STRY did not alter the NMDA response.