Immunohistochemical studies of bone from individuals with osteogenesis imperfecta (OI) type II, OI type III, or OI type IV demonstrate a similar pattern, but varying extent, of the abnormal presence of interstitial collagens in bone matrix. OI type II bone had nests of cartilage with type II collagen, and significant type III collagen in the bone matrix. In OI types III and IV, type II collagen was present only in epiphyseal cartilage but bone still contained type III collagen. These findings resembled those in developing fetal bone indicating the "immature" nature of OI bone.