THE LIPODYSTROPHIES, a group of disorders characterized by loss of adipose tissue in various distributions, are associated with an assortment of metabolic abnormalities, predominately insulin resistance, hypertriglyceridemia, and fatty liver. To better understand the role of adipose tissue in the development of diabetes and obesity, transgenic mice, or gene knockout mice, have been produced that mimic the human forms of lipodystrophy. The study of these mice and adipocytes in general, which are now known to produce a variety of bioactive molecules, has transformed the view of the adipocyte from a passive storage cell to a more complex one functioning as a secretory and endocrine tissue that may also be linked to the immune system.