Rapidly progressive periodontitis (RPP) results from the interaction between the periodontal microflora and the host. Stress is believed to play an important role in determining host responses, and it has been proposed that hyperactivity of host defense mechanisms significantly increases tissue destruction typical for this disease. During a period of four months we have diagnosed 20 patients with acute RPP, all of them active participants in battles of the Croatian liberation war with posttraumatic stress disorder (PTSD) related symptoms. In these patients we analyzed biochemical parameters in unstimulated saliva and performed microbiological analyses of periodontal pockets. These findings were compared with those of patients with adult periodontitis (AP), edentulous and healthy persons, none of whom participated in the war. Persons with AP had reduced concentrations of host humoral defense factors in saliva (C-reactive protein, C3 component of complement, and aplha alpha 2-macroglobulin), while patients with RPP had increased concentration of interleukin-6 (IL-6). IL-6 is released by host inflammatory cells and is a mediator of bone resorption. Actinobacillus actinomycetemcommitans and Peptostreptococcus were more frequently isolated from patients with RPP. We interpret these results as indicators of the importance of stress in the causation of RPP, with host inflammatory hyperactivity playing an important role in tissue destruction, specially alveolar bone resorption possibly caused by increased local levels of IL-6.