Antimicrobial agents, applied either professionally or delivered from dentifrices or mouthwashes, could reduce caries by controlling plaque formation, suppressing cariogenic species, or by inhibiting bacterial metabolism. Chlorhexidine has proven anticaries activity; other agents might also prevent caries by means of their antiplaque properties. Sugar substitutes stabilize the microflora by reducing the number of acid challenges to plaque and stimulating saliva flow; some also have antimicrobial properties, especially against mutans streptococci. Vaccines have been prepared from purified antigens of mutans streptococci. These vaccines confer protection in non-human primates, but have yet to be tested in a human clinical trial.