The purpose of the present study was to examine the composition of the oral microbiota in subjects who had previously demonstrated to develop either a weak or strong response to experimental gingivitis. For this study, subjects were selected from a pool of 25 individuals who had participated twice in an experimental gingivitis trial. Out of these 25 panellists, 6 subjects were selected who had developed 2X a weak gingival inflammatory response and 7 subjects who had developed 2X a strong gingival inflammatory response. Approximately 9 months after the 2nd experimental gingivitis trial, we evaluated the clinical condition and the prevalence of a panel of selected oral micro-organisms in these subjects. The subjects were clinically examined for the presence of plaque, bleeding, pocket depth and loss of attachment. For the microbiological evaluation, samples were taken from the mucous membranes, subgingival sites and saliva. Samples were analyzed for the presence of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Peptostreptococcus micros, Actinomyces spp., Fusobacterium nucleatum, Campylobacter rectus, spirochaetes and motile rods. Clinical evaluation showed that most subjects had a relatively healthy periodontal condition. No clinically significant differences could be detected between the weak and strong responding groups. The microbial evaluation showed absence of A. actinomycetemcomitans, P. gingivalis and P. micros in all subjects in either group. Analysis of the microbial data for the weak and strong responding group showed no differences between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)