Actinobacillus actinomycetemcomitans has been implicated in the pathogenesis of several forms of early onset and refractory adult periodontitis. Early diagnosis of colonization of the oral cavity might be of importance in order to initiate preventive measures. The aim of the present study was to determine the potential diagnostic value of oral mucosal and salivary tests to identify, among healthy young men with no or minor periodontal disease, individuals colonized by A. actinomycetemcomitans. Two hundred and one male recruits, 18-25 yr of age, took part in the present study. Mean values of periodontal parameters suggested only minor periodontal disease. Of the sites, 64.8 +/- 17.6% (mean +/- SD) had a periodontal probing depth (PPD) of 1 or 2 mm, only 1.6 +/- 2.9% deep sites of > or = 5 mm were detected. More than 1000 subgingival and extracrevicular samples were selectively cultivated for A. actinomycetemcomitans. The organism was isolated in 55 subjects (27%). The odds for presence of at least 1 deep site of 5 mm was increased by a factor 1.99 if A. actinomycetemcomitans, could be recovered. In identifying subjects colonized by A. actinomycetemcomitans, diagnostic test parameters sensitivity and predictive value for a negative test were 74.5 +/- 5.9% and 91.1 +/- 2.3%, respectively, for both saliva and dorsum of tongue samples. In contrast, pooled subgingival plaque from mesial surfaces of 1st molars was only 34.5 +/- 6.4% sensitive; the negative predictive value was 80.2 +/- 3.0%. The results point to a high diagnostic value of oral mucosal and especially saliva samples to identify young adult individuals colonized by A. actinomycetemcomitans.