Dehydroepiandrosterone (DHEA), a hormone produced by the adrenal glands, is the precursor for the production of estrogens and testosterone, and is therefore normally present in significantly greater quantities than all the other steroid hormones. It is mostly found in the circulation in the form of its sulfate ester, DHEA sulfate (DHEA-S), which is measured in blood spot in preference to free DHEA because its circulating levels are higher and more stable. Its production is highest in the late teens to early 20s, and declines gradually with age in both men and women. Levels of DHEA-S reflect adrenal gland function. Low DHEA-S indicates adrenal insufficiency and/or androgen deficiency, and can be associated with reduced libido and general malaise. High DHEA-S levels are seen in hyperadrenal states such as congenital adrenal hyperplasia, and in polycystic ovarian syndrome; high levels in women are associated with masculinizing effects because of its local metabolism to testosterone. DHEA supplementation has been successfully used to treat adrenal insufficiency and can restore normal levels of testosterone in women with androgen deficiency, particularly as a consequence of removal of the ovaries. Because of its conversion to potent estrogens and androgens, levels should be closely monitored during supplementation to avoid excess. The blood spot reference range for DHEA-S in women is 40—290 µg/dL, and for men 70—325 µg/dL.