Loss of alveolar bone is associated with chronic gingival inflammation and periodontal disease. Previous studies have shown that both healthy and inflamed gingival samples can produce bone-resorbing factors when cultured. The major objective of this study is to gain insight into some aspects of the mechanism of bone loss in periodontal disease, by determining as closely as possible which structural components of inflamed gingiva are associated with in vitro bone resorbing activity. The gingival tissues to be examined will come from beagle dogs in various stages of controlled inflammation, both with and without radiographic evidence of alveolar bone loss. Bone resorbing activity will be measured in freeze dried, microdissected, weighed samples, by means of 45Ca release from labelled fetal rat bones in culture. The results, expressed as the ratio of 45Ca released in each cultured and that remaining in the test bone, will be compared with non-inflamed control tissue and statistically analyzed for validity or otherwise. Although the main part of the study will be carried out on tissue from dogs, in the final phase of the study the bone resorbing activity of human gingiva will be compared with that found in the animal model. A comparison will be made of bone resorbing activity in both adult and childhood gingivitis.