A clinical study of the distribution of different types of bone defects in chronic periodontitis was carried out on 30 patients. An analysis of 176 defects suggests that their distribution reflects the original morphology of the alveolar bone. The role of function as a determinant of that morphology is examined. While there appears to be a relationship between functional stress and the phylogenesis of the bone, there is no direct relationship between function and ontogenesis. A study of growth remodelling of the mandible in several animals indicates that the pattern of activity is dictated by a drive to achieve a mature form which is the expression of the genetic endowment. Normal function and normal muscle stress are part of the environment in which complete growth can take place, but they do not appear to play a more active role in determining the form of growth; abnormal function does not allow normal growth to take place. The relationship between functional stress and the morphology and activity of the mature bone is not clear. Osteoporosis of age, as measured by the metacarpal index in 101 patients with chronic periodontitis, did not appear to be significantly related to the bone loss score. However, in 54 females patients, aged 35-45 years, a significant correlation was found between the metacarpal index and a "rapidity of bone loss" score.