In this study, we investigate the prevalence of selected periodontal pathogens on the oral mucous membranes before and after full-mouth tooth extractions in patients with severe periodontitis. 8 patients were microbiologically examined 2 x before and 2 x after extraction; several locations on the oral mucous membranes, saliva, supra- and subgingival plaque, were sampled. Besides their presence in subgingival plaque, we detected before extraction on the mucous membranes Actinobacillus actinomycetemcomitans in 2 patients (mean 0.03%), Porphyromonas gingivalis in 6 patients (mean 9%), and Prevotella intermedia (mean 2%) and other Prevotella species (mean 7%) in all patients. At 1 and 3 months after extraction, A. actinomycetemcomitans and P. gingivalis could not be detected in any of these patients on the oral mucous membranes and in saliva, while from all patients still P. intermedia (mean 3%) and the other blackpigmented Prevotella species (mean 4%) could be isolated. These results indicate that the preferable habitat for A. actinomycetemcomitans and P. gingivalis is dental plaque in subgingival lesions. P. intermedia and the other blackpigmented Prevotella species can colonize the oral mucous membranes of edentulous patients irrespective of the presence of a subgingival microflora. We speculate that in periodontal patients the colonization of mucous membranes with P. gingivalis and A. actinomycetemcomitans is transient in nature and most likely the result of dissemination from the subgingival microflora. Thus it seems unlikely that edentulous patients constitute a reservoir of infection of P. gingivalis A. actinomycetemcomitans.