The human mouth providesa suitablehabitat for numerousbacterialgenera. Anaerobic genera or genera that include anaerobic members found in the oral cavity are Actinomyces, Arachnia, Bacteroides, Bifidobacterium, Eubacterium, Fusobacterium, Lactobacillus, Leptotrichia, Peptococcus, Peptostreptococcus, Propionibacterium, Selenomonas, Treponema, and Veillonella. The incidence of anaerobes varieswith age of the individualand with specific sitessampled. In edentulous infants, the incidence of anaerobes is relatively low. In adults, anaerobes are invariably present but are more prevalent in samples from the gingival sulcusthan they are in samples from the gingival margin, tooth surfaces, buccal mucosa, tongue, or saliva. In samples from the healthy gingival sulcus, anaerobic, gram-positive bacilli are found in the range of 5%–14%; gram-negative bacilli in the range of l3%–29%; Veillonella in the range of 2%–8%; and gram-positive cocci in the range of 1%–15% of the cultivable flora. From marginal plaqueand plaque from the tooth surface, gram-positive bacilli,gram-positive cocci,and Veillonella appear to be the predominant anaerobes. In saliva, Veillonella are the most numerous anaerobes.