Noncollagenous proteins and proteoglycan from the bone and dentin of affected and normal half-siblings neonatal calves with the Australian variant of bovine osteogenesis imperfecta (BOI-A) were quantitated. In contrast to a clinically similar syndrome of BOI in the progeny of a second progenitor bull identified in Texas (BOI-T), osteonectin and bone sialoprotein levels were normal in the affected BOI-A bone, and dentin phosphophoryn levels were normal in affected BOI-A teeth. However, bone proteoglycan in the affected BOI-A calves was depleted to one-third of the level found in normal siblings, a finding qualitatively similar to the depletion of bone proteoglycan in the BOI-T syndrome. These results suggest that quantitation of noncollagenous proteins and proteoglycans may be a useful technique for differentiating clinically similar syndromes of OI in man.