Most of the diseases with which dentists must deal with are related to microbial plaque and bacterial infection. The mechanical removal of supra- and subgingival plaque by the patient and by the dentist respectively, is time consuming and exacting, furthermore it is not one hundred per cent successful. There has been extensive search for many years for chemical agents that could supplement or even substitute mechanical plaque removal. Many chemical agents delivered in different ways were tested. Chemotherapeutics of various modes of action have to meet pharmacokinetic and biological requirements. Apparently the ideal anti-plaque agent is not yet available, so that they should be reserved for well defined clinical situations and short--or medium--term application.