Rett syndrome (RTT) is a severe form of mental retardation, which is caused by spontaneous mutations in the X-linked gene MECP2. How the loss of MeCP2 function leads to RTT is currently unknown. Mice lacking the Mecp2 gene initially show normal postnatal development but later acquire neurological phenotypes, including heightened anxiety, that resemble RTT. The MECP2 gene encodes a methyl-CpG-binding protein that can act as a transcriptional repressor. Using cDNA microarrays, we found that Mecp2-null animals differentially express several genes that are induced during the stress response by glucocorticoids. Increased levels of mRNAs for serum glucocorticoid-inducible kinase 1 (Sgk) and FK506-binding protein 51 (Fkbp5) were observed before and after onset of neurological symptoms, but plasma glucocorticoid was not significantly elevated in Mecp2-null mice. MeCP2 is bound to the Fkbp5 and Sgk genes in brain and may function as a modulator of glucocorticoid-inducible gene expression. Given the known deleterious effect of glucocorticoid exposure on brain development, our data raise the possibility that disruption of MeCP2-dependent regulation of stress-responsive genes contributes to the symptoms of RTT.