Growth hormone (GH), a well-known anabolizing agent, not only plays a physiological role in childhood by promoting longitudinal growth, but also it remains to be secreted during adult life. Many aspects on physiological and pharmacological actions of this hormone in adulthood have been clarified in the last years. GH induces the biosynthesis of insulin-like growth factor I (IGF-I), a peptidic compound that acts as a mediator of indirect actions of GH. In GH deficient adults, exogenous GH administration produces a decrease in adipose mass which is accompanied by an increase in lean body mass, mainly due to an enlargement of muscle cell mass. Sodium and water retention has been also described. An augmentation in muscle strength, basal metabolic rate and nitrogen retention by action of GH are expressions of the potential anabolizing effects of this hormone in adult life. Glucose tolerance is decreased by GH, and this effect is accompanied by a decrease in peripheral utilization of glucose and an increase in insulin secretion. GH behaves as a lipolytic hormone and gives rise to an increase in resistance to the lipogenetic action of insulin. GH treatment increases plasma levels of bone Gla protein and other marker of osteoblastic activity, what suggests a physiological role of GH in bone turnover regulation. Many other organic functions are also affected by GH administration.