The purpose of this study was to determine whether glycine is effective in correcting the age-related change in the N-methyl-D-aspartate (NMDA) receptor complex. Autoradiographic analysis of [3H]MK801 and NMDA-displaceable [3H]glutamate binding was performed with 0, 10, 30 and 100 microM glycine on brain tissue from 3-, 10-, and 24-30-month-old C57B1 mice. Glycine, even at 10 microM, enhanced binding to both the NMDA and MK801 binding sites in all age groups. Glycine was not able to reduce the absolute difference in [3H]glutamate binding to NMDA sites between 3- and 24-month-olds. Low micromolar concentrations of glycine exacerbated the aging difference in [3H]MK801 binding between young and old mice, but 100 microM glycine produced smaller aging differences that were similar to those seen with no glycine. This study suggests that glycine may enhance NMDA receptor function in old animals, but it does not appear to correct the underlying problem with the NMDA receptor in aged animals.