The invention provides methods for treating or preventing bone degenerative disorders. The disorders treated or prevented include, for example, osteopenia, osteomalacia, osteoporosis, osteomyeloma, osteodystrophy, Paget's disease, osteogenesis imperfecta, and bone degenerative disorders associated with chronic renal disease, hyperparathyroidism, and long-term use of corticosteroids. The disclosed therapeutic methods include administering to a mammal an inhibitor of GDF-9 or BMP-15 in an amount effective to: (1) treat or prevent a bone degenerative disorder; (2) slow bone deterioration; (3) restore lost bone; (4) stimulate new bone formation; and/or (5) maintain bone mass and/or bone quality. The invention also provides methods for administering a GDF-9 agonist or a BMP-15 agonist to treat a bone disorder characterized by increased bone density or mass.