A reduction in the adherence of oral streptococci was observed after topical application of aluminum ions to standardized dentin test pieces whereas pyrophosphate and tripolyphosphate seemed to inhibit the adherence after incorporation in the incubation solution. A pronounced effect was recorded after topical application of surfactants with the positively charged primary amino group as end group. Hydrofluorides of several such aliphatic amines effectively reduced the number of colony-forming units washed off from the test pieces. Also the free base of hexadecylamine showed a similar effect. Inhibition of adherence was also obtained with long chain esters of lysine, with an optimum at 16 carbon atoms in the alcohol group. These compounds have the advantage of being built up from molecules known to the body.