The periodontal status of maxillary first molars in 284 young adults demonstrating near-health to early disease was evaluated, and supragingival and subgingival plaque samples were collected. Plaque samples were processed anaerobically, enumerated microscopically for bacterial morphotypes, and cultivated on various media to enumerate the microflora. Although haemophili were ubiquitous (recovered in 98.5 and 96.2% of the supragingival and subgingival plaque samples, respectively), 50% of the respective samples had proportions of less than or equal to 1.5% and less than or equal to 0.33% total Haemophilus spp. based on total cultivable microflora. To study the distribution of Haemophilus spp., 377 colonies were identified from modified chocolate agar (selective for oral haemophili) from 14 supragingival and corresponding subgingival samples from 14 subjects. The most prevalent species, Haemophilus parainfluenzae, was found in significantly higher proportions, based on total haemophili on modified chocolate agar, in supragingival and subgingival samples from teeth with shallower probing depths (less than or equal to 3.0 mm) versus deeper probing depths (greater than or equal to 3.0 mm). Additional statistically significant findings included Haemophilus segnis in higher proportions in supragingival samples from deeper sites, Haemophilus aphrophilus in higher proportions in subgingival samples from deeper sites, and Haemophilus paraphrophilus in higher proportions in subgingival samples from shallower sites. Scatter diagrams illustrating the bivariate distributions of proportions of haemophili with proportions of dark-pigmented Bacteroides spp., spirochetes, and streptococci demonstrated that high proportions of haemophili were never recovered from sites with high proportions of Bacteroides spp. or spirochetes. All levels of haemophili, however, were recovered from sites with all levels of streptococci. Two potential systems for interpreting haemophili data were hypothesized for predicting periodontal probing depths. There was highly significant agreement between the two systems. Small but statistically significant correlations were found between the gingival index, probing depth, and attachment level, and proportions of total Haemophilus species in the respective samples.