This study evaluated the rubber dam as an infection control barrier during standard restorative procedures. Microbial collection was performed during preparation and placement of amalgam and composite resin restorations with and without the rubber dam, and during handpiece and air-water syringe spraying with and without the rubber dam. The results showed a significant reduction in microorganisms with the use of the rubber dam--70% to 88% and 95% to 99%, respectively; and 90% to 98% when all data were combined. These results indicate that using the rubber dam is a method of reducing microbial contamination at the primary source. Used with gloves, mask, and protective eyewear, the rubber dam provides an excellent barrier to the potential spread of infectious disease in the dental office.