1. In osteogenesis imperfecta the bones are brittle but the teeth, whose dentine contains the same genetic collagen as bone (type I), may be clinically normal.
2. To investigate this paradox we have measured the amino acid composition of insoluble dentine collagen from 16 deciduous and 18 permanent teeth in control subjects and in 59 patients with different forms of osteogenesis imperfecta.
3. In 55 of the patient samples significant differences from normal were found, especially in the number of lysine residues, and in the relative amounts of hydroxylysine to lysine.
4. These results demonstrate the high frequency of biochemical abnormalities in osteogenesis imperfecta. They also suggest that classifications of this disorder based on the presence or absence of clinical dentiogenesis imperfecta are likely to be unsound.