The purpose of this study was to determine the antimicrobial activity of one prescription and two commercially available over-the-counter mouthrinses and positive and negative controls against bacteria commonly found in the oral cavity. The bacteria used in this study were Streptococcus mutans, Streptococcus sanguis and Actinomyces viscosus. Sterile discs which were treated with the mouthrinses were placed on agar plates along with the controls. Zones of microbial inhibition were measured in millimeters after 48 hours. The results indicated that all of the mouthrinses demonstrated antimicrobial activity against the bacteria tested. Herbal Mouth and Gum Therapy mouthrinse, containing natural ingredients, produced the largest zones of microbial inhibition when compared to Listerine against all three of the bacteria tested. Herbal Mouth and Gum Therapy mouthrinse produced larger zones of microbial inhibition when compared to Peridex against two of the three bacteria tested, and produced similar zones of inhibition against the third bacteria.