The purpose of this continuing study is to determine the prevalence and progression of gingivitis, epithelial attachment loss, and bone loss in a group of adolescents residing in the U.S. A longitudinal study is in progress of Navajo adolescents to investigate microbiologic, systemic and other factors that may contribute to the high prevalence of disease. Two hundred twentysix subjects were examined in February 1986, 1987 and 1988 using the same clinical and radiographic techniques. Subgingival plaque samples were obtained from all first molars and analyzed for A. actinomycetemcomitans, B. gingivalis and B. intermedius. Analyses of first year data indicate that the combination of calculus, gingival bleeding and B. intermedius gave the most parsimonious explanation of the presence of attachment loss. Bite-wing radiographs from all three years have now been read for evidence and quantification of alveolar bone loss using image enhancement software (JAVA). The proportion of subjects and sites infected with B. gingivalis had increased substantially by the last examination, while the prevalence of A. actinomycetemcomitans and B. intermedius remained fairly constant. Multiple logistical regression analyses are in progress to study the joint effects of clinical and microbiologic variables on bone loss and attachment loss.