Androgens, in combination with a genetic susceptibility, have been demonstrated to be required for the development of androgenetic alopecia. Disturbances in androgen metabolism or target organ sensitivity are thought to underlie the pathophysiology of the condition. Observations of patients with disorders of androgen metabolism or function have determined the basic physiology involved in regulation of hair growth by androgens at selective body sites. More recently, in vitro studies of scalp skin and hair follicles have begun to define specific alterations in androgen metabolism at the local level that may play a key role in pathogenesis. The prominent role of 5-reductase in these studies suggests that inhibitors of this enzyme may provide new therapeutic opportunities for patients with androgenetic alopecia.