The AR (androgen receptor) is a ligand-activated transcription factor that mediates the action of the steroids testosterone and dihydrotestosterone. Alterations in the AR gene result in a number of clinical disorders, including: androgen-insensitivity, which leads to disruption of male development; prostate cancer; and a neuromuscular degenerative condition termed spinal bulbar muscular atrophy or Kennedy's disease. The AR gene is X-linked and the protein is coded for by eight exons, giving rise to a C-terminal LBD (ligand-binding domain; exons 4-8), linked by a hinge region (exon 4) to a Zn-finger DBD (DNA-binding domain; exons 2 and 3) and a large structurally distinct NTD (N-terminal domain; exon 1). Identification and characterization of mutations found in prostate cancer and Kennedy's disease patients have revealed the importance of structural dynamics in the mechanisms of action of receptors. Recent results from our laboratory studying genetic changes in the LBD and the structurally flexible NTD will be discussed.