ALTHOUGH dental plaque is often mentioned in dental literature, its chemical composition has received little attention. Current literature frequently refers to “dentobacterial plaque” with the implication that it consists principally of bacteria. Manly1, however, brushed teeth with a detergent prior to the collection of a film, which he called “brown pellicle”. This material was free from microorganisms and was considered to be principally protein. Vallotton2 studied a similar deposit and found 8.9 per cent nitrogen and 24.8 per cent ash. Earlier, Dobbs3 had also detected carbohydrate and lipid materials, in addition to protein and inorganic substances.