The mechanisms of action of antimicrobials have been based in the past on in vitro data obtained from laboratory experiments performed on pure cultures of bacteria. A more complete understanding of oral antimicrobials and their mechanisms of action will results from testing of agents in systems that more closely resemble environmental areas existing in the oral cavity. It is proposed that mechanisms of drug action be studied with a drug held at suboptimal (sublethal) concentrations for short periods and in a dynamic environment that resembles the mouth. Adequate guidelines provided by the American Dental Association Council on Dental Therapeutics are available and have helped to determine the efficacy of these agents over long periods in appropriate populations.