Androgens exhibit a wide range of effects on the development, maintenance and regulation of male phenotype and reproductive physiology in males. The androgen receptor (AR) is a member of the steroid superfamily of ligand-dependent transcription factors. ARs bind active testosterone (T) and dihydrotestosterone (DHT). The rates of association and dissociation of T are about 3 times more rapid than those of DHT. This difference in binding kinetics may account for the different physiological effects of T and DHT. Androgen binding results in an at least 6-fold increase in androgen receptor stability.