The aerosols generated in an operating room during surgery were simulated in the laboratory by using a variety of common surgical power tools. A Stryker bone saw, a Hall drill, and a Shea drill were used on bone, and a Bovie electrocautery was used in both the cutting and coagulation modes on tendon, all in the presence of a thin film of blood. A 10-stage, low-pressure cascade impactor was used to determine the particle size distribution of each aerosol, and Hemastix was used to assess the hemoglobin content of each particle size fraction. The same assessment was done for another series of blood aerosols that had previously shown the ability to infect human T-cell cultures. All of the tools tested produced blood-containing aerosol particles in the respirable size range (less than 5 microns). Because surgical masks offer little protection against such particles, personal sampling is indicated to define the risk of exposure to bloodborne pathogens by this route.