Bacteria-containing spray (including both aerosols and splatter) has been shown to be a potential source of contagion in the dental environment. Bacterial air contamination increases during dental treatment; this is especially true during ultrasonic scaling procedures. This in vivo investigation evaluated the amount of bacteria-containing spray produced during ultrasonic scaling of 15 patients when using a suction-type aerosol reduction device (ARD) and/or a preoperative 0.12% chlorhexidine gluconate (CHX) antimicrobial rinse. When the study protocol was followed, the use of either an ARD or a CHX rinse produced significant bacterial reductions during ultrasonic scaling compared to the control. The use of an ARD produced the greatest bacterial reductions. Combining the ARD and the CHX rinse was no more effective than the use of an ARD alone.