GH AFFECTS several tissues including liver, muscle, kidney, and bone. GH effects on muscle and kidney have recently been extensively reviewed in Endocrine Reviews by Florini et al. (1) and Feld and Hirschberg (2). Since GH has important effects on skeletal tissues, our focus in this article will be on our current understanding of GH effects on bone. A large increase in bone mass occurs during childhood and puberty via endochondral bone formation. A gradual increase in bone mass is then seen until peak bone mass is reached at 20–30 yr of age. Subsequently, bone mass decreases with an accelerated bone loss seen in females after menopause. Bone remodeling is regulated by a balance between bone resorption and bone formation. In this process GH is known to play a role (3–7). A net gain of skeletal mass due to new bone formation caused by GH was first shownin adult mongrel dogs (8). After treatment with GH for 3 months a 2% increase in cortical bone mass, as assessed by histomorphometry, was found