APPROXIMATELY 60 yr ago, Houssay and his colleagues (1) described hypersensitivity to insulin in hypophysectomized (hypox) animals. Further work documented a primary effect of GH in this phenomenon (1). Over the ensuing years, numerous investigators have sought to define the role of GH in carbohydrate and lipid metabolism. Unfortunately, no unified picture has emerged. Both insulin-like and antiinsulin-like effects have been documented, although the physiological significance of the former is uncertain. Major controversies surround the relationship between structure and function of the GH molecule. Indeed, some believe that most of the reported effects of GH are due to contaminants in the hormone preparation. With two exceptions (2, 3), reviews in this area (4–10) have focused mainly on the author's own work in a circumscribed field; e.g. in vivo effects after GH administration (6, 7, 9), tissue effects in vitro (5, 7), or effects on lipolysis (4, 8,10). Furthermore, these reviews were published more than 10 yr ago.