AL 082D06 (D06) binds specifically to GR with nanomolar affinity. Addition of AL 082D06 causes a dose-dependent decrease in transcriptional activation from the MMTV:Luc reporter stimulated with half-maximal DEX concentrations. AL 082D06 acts to antagonize reporter activity using several glucocorticoid-responsive promoter- reporter systems including the 3-kb tyrosine amino transferase (TAT) promoter and less complex promoters comprised of isolated glucocorticoid response element (GRE) sequences. AL 082D06 competes with ³ H-Dex for baculovirus-expressed GR with nanomolar affinity. Other intracellular receptors (AR, ER, PR, and MR) have no affinity for AL 082D06 in a similarly structured binding assay with the appropriate receptor and tritiated ligand (>2500 nM). AL 082D06 has no activation efficacy on the progesterone, androgen, mineralocorticoid, retinoid, glucocorticoid, or estrogen receptors. AL 082D06 is very efficacious at antagonizing GR activity but exhibits much weaker efficacy when tested against the other steroid receptors in contrast to the reference antagonists used as controls.