Growth deficiency is a cardinal feature of severe Osteogenesis Imperfecta (OI) and a frequent feature of mild to moderate forms of this disease. Despite the prevalence of short stature among people with OI, few studies have examined treatment options for this feature of OI. Recombinant human growth hormone (rGH) is a treatment for growth deficiency which we have investigated. In our initial studies we have found that many OI children are responsive to rGH especially those with type IV OI. The purpose of this protocol is to examine the effect of growth hormone treatment on linear growth of children with types III and IV OI and correlate growth responsiveness with growth hormone-somatomedin axis and histomorphometry parameters of OI bone.