OBJECTIVE Hypertensive and other effects of excess glucocorticoids might be in part mediated by the suppression of endothelial nitric oxide synthase (eNOS) expression. We studied the transcriptional and biochemical mechanisms that mediate or modulate the suppression of eNOS expression by glucocorticoids. RESULTS We found that a mere three-fold increase in the concentration of the natural glucocorticoid cortisol (from 30 to 100 nmol/L) significantly decreased the expression level of eNOS in human endothelial cells. Deletion analysis of the eNOS promoter indicated that the segment within -119 bp upstream from the transcription start site was significantly involved in the effect of cortisol. Site-directed mutagenesis and chromatin immunoprecipitation analyses demonstrated the presence of a suppressive glucocorticoid response element (GRE) at -111 to -105 bp. 11 beta-hydroxysteroid dehydrogenases (11 beta-HSD) catalyse the interconversion of active and inactive glucocorticoids. The suppression of 11 beta-HSD2 using small interfering RNA markedly exacerbated the inhibition of eNOS by cortisol. The suppression of 11 beta-HSD1 abolished the inhibition of eNOS expression by cortisol. CONCLUSIONS We identified the first GRE in the eNOS promoter region and demonstrated that endogenous 11 beta-HSD1 and 11 beta-HSD2 play significant and distinct roles in modulating the effect of glucocorticoids on eNOS expression.