The purpose of this investigation was to study the microflora of severe, moderate and minimal periodontal lesions, in young adults with rapidly progressive periodontitis (RPP). Subgingival plaque samples were taken from 142 periodontal lesions in 10 young adults aging 25 to 35 years. The examination of the subgingival microflora indicated that certain species, including Porphyromonas gingivalis, Bacteroides forsythus, Fusobacterium nucleatum, Actinobacillus actinomycetemcomitans, and Campylobacter species were found to be predominant in severe periodontal lesions. B. forsythus, P. gingivalis, Prevotella intermedia, F. nucleatum, Capnocytophaga ochracea, were predominant in medium lesions while Streptococcus species and Actinomyces species, C. ochracea, Haemophilus segnis and Veillonella parvula, were found in higher levels in minimal periodontal lesions.