High intraoral load of A. actinomycetemcomitans in subjects with no or minimal periodontal disease may induce subtle changes in clinical periodontal conditions. The aim of the present study was to compare, at a site level, clinical conditions in two groups of young adults with plaque-induced gingivitis. In one group, more than 20% subgingival sites harboured cultivable A. actinomycetemcomitans (n=9), whereas in the other group, the organism was present in 20% or fewer subgingival plaque samples (n=8). Whereas no overt differences in clinical conditions could be ascertained, on average, the association between the presence of subgingival plaque and bleeding upon probing was considerably stronger (Mantel-Haenszel's common odds ratio RMH and 95% confidence interval 3.903, 2.951-5.165, P<0.001) in subjects with only a few subgingival sites harbouring A. actinomycetemcomitans as compared to subjects with a widespread intraoral distribution of the organism (R(MH)=1.637, 1.226-2.184, P<0.001). Since the proportion of sites not bleeding upon probing in the presence of supragingival plaque was slightly elevated in these subjects, the present findings may suggest a suppressed inflammatory reaction on supragingival plaque in the presence of a pronounced intraoral load of A. actinomycetemcomitans.