The present study was designed to determine whether the changes that occur during aging in the expression of the N-methyl-D-aspartate (NMDA) receptor and two NMDA receptor subunits, zeta1 and epsilon2, are a continuation of developmental processes and whether protein and mRNA expression patterns of the subunits are similar across the lifespan. The prefrontal/frontal cortex of C57BL/6 mice of eight different ages (7-8, 13-15, 30-32, 49-53, and 70-72 days and 4.5, 11, and 25 months of age) were used to examine NMDA-displaceable [(3)H]glutamate binding and mRNA in tissue sections and mRNA and protein from homogenates. The lateral prefrontal/frontal cortex of C57BL/6 mice showed more significant declines in density of agonist binding to NMDA receptors during both development and aging than the medial cortex. Changes in mRNA expression for the epsilon2 subunit across the lifespan appeared to be related to the changes in NMDA receptor binding in the lateral cortex, even though the protein expression of the epsilon2 subunit did not show the same pattern of expression as the mRNA during development. The changes in epsilon2 subunit mRNA expression during adult aging may be a continuation of developmental processes, but there was also evidence that expression levels plateaued during early adulthood. The developmental expression of the zeta1subunit in the prefrontal/frontal cortex was influenced by gender and there was no significant effect of adult aging on either the protein or mRNA expression of this subunit. Determining how the expression of the NMDA receptor and its subunits change throughout the lifespan can help us to better understand the processes affecting the receptor during aging. These results should be useful for designing interventions into the aging process to repair or prevent changes in the NMDA receptor and its associated functions, such as learning and memory.