Growth hormone (GH) is a well established participant in several complex physiological processes including growth, differentiation, and metabolism. Recombinant human GH is a drug that has been approved for use for several clinical conditions where the action of GH is diminished or completely lacking. Thus there is considerable interest in developing novel drugs that modify the function of GH. Only in the last several decades have the detailed structural features of GH along with its interaction with its receptor been elucidated. In this review we summarise the basic structural and functional properties of GH, its receptor and their interaction. In addition, we discuss the discovery and development of an effective GH receptor antagonist, pegvisomant, and summarise potential therapeutic uses of this drug.