Test specimens of amalgam, gold, porcelain, heat-cured acrylic resin, and human enamel were made to fit into cavities prepared in acrylic pontics of maxillary bridges. One side of the specimen was in close contact with the mucosa. Plaque was allowed to accumulate on the specimens for 27 to 48 days, and adherent bacteria were then quantified by cultivation on selective and non-selective media. The inflammatory status of the mucosa overlying the specimens was monitored by exudation measurements. Lower total numbers of bacteria were recovered from acrylic specimens than from the other materials used, including enamel. There were also significant subject differences in bacterial recovery. Test specimens in contact with inflamed mucosa yielded less total numbers of bacteria, but higher numers ofStreptococcus mutans, than did specimens exposed to mucosa with no or negligible exudation.