Androgen deprivation can be achieved surgically with orchiectomy, or using some form of drug treatment. Current approaches to AD utilize leutinizing hormone releasing hormone (LHRH) agonists. These act by continuous stimulation of the anterior pituitary resulting in inhibition of leutinizing hormone (LH) secretion, and hence a fall in testicular production of testosterone. Although AD is clinically effective in the majority of patients, studies have shown that extratesticular sources of testosterone represent an important alternative source of androgen stimulation in a significant proportion of prostate cancer patients. As much as 10% of baseline circulating testosterone remains in castrate men, due to the peripheral conversion of adrenal steroids to testosterone. Increased levels of androgen receptor confer resistance to antiandrogens in prostate cancer xenograft models. This could result in amplified signal output from circulating low levels of adrenal androgens and suggests a role for agents that target the adrenal androgen synthesis pathway.