Polydimethylsiloxan (silicone oil) adsorbs to solid surfaces and to teeth because of its low surface tension, forming a thin, resistant layer. Triclosan is a lipid-soluble, antibacterial substance which is added to toothpastes and mouthwashes to inhibit plaque. Triclosan can be dissolved in silicone oil, conferring an antibacterial property on the layer of silicone oil which forms on solid surfaces. The aim of the present study was to determine whether a toothpaste containing triclosan/silicone oil has any effect on established gingivitis in a test panel of 33 teenagers. This toothpaste and a placebo paste were randomly distributed to the panel, and the number of gingival bleeding points was recorded. No instruction in oral hygiene was given. The panel was then examined 4 wk later and the number of bleeding points again recorded. It was found that the reduction in bleeding points was significantly higher in the group which had used the triclosan/silicone oil paste than in the placebo group. Deposition of a lipid-soluble, antibacterial agent in a layer of silicone oil which adsorbs to the tooth surfaces because of its physical properties represents a new and promising principle in preventive dentistry.