The interaction of ethanol with glycine at the N-methyl-D-aspartate (NMDA)-activated ion channel was investigated in voltage-clamped rat cultured hippocampal neurons. As shown previously, glycine increased, and ethanol inhibited, the NMDA-activated current in these cells. Concentration-response data for glycine (0.1-100-mu-M) indicate that the inhibition of NMDA-activated current by ethanol does not involve a competitive interaction with glycine. Thus, ethanol appears to inhibit NMDA-activated current at a locus different from the glycine modulatory site.