Wide variations in the radiopacity of the jaws are known to occur among individuals. The radiopacities of the lip and mandible were measured on over 150 patients and were correlated with the thickness of the tissue involved and the facial type and age of the patient. Radiopacity was found to increase with thickness of bone or soft tissue. The radiopacities of the individual of lean facial type and of patients aged 50 years and older increased very rapidly with increasing thickness of bone, whereas those for individuals of the obese facial type and of children aged 15 yrs. and younger increased much more slowly. The radiopacity of the lip tissue increased with thickness of the tissue but appeared to be independent of age, sex, facial type or race. The factors which cause one individual to be more radiopaque than another are contained in the alveolar process. Data are presented which indicate how the voltage applied to the x-ray tube should be adjusted to produce radiographs of uniform density on a variety of types of patients.