Powered dental instruments applied to whole-blood in a typodont field of operation generated aerosols of red blood cell and hemoglobin-tinged plasma at rates ranging from 0.003 to 2.2 microL of plasma per minute with particle sizes ranging from 0.06 to 13 microns and half-lives of 35 minutes to 17 hours. Particles 0.06 to 0.38 microns were plasma spheroids that contained no detectable hemoglobin or red blood cell fragments. Particles 0.66 to 13 microns were mostly plasma spheroids, only a small fraction of which contained whole and fragmented red blood cells. All the recovered particles physically could contain the 0.042 microns hepatitis B virus, could be inhaled, and 20 to 100% of them could be retained in the human respiratory system. Of 0.06 to 2.5 microns plasma aerosol particles, 15-83% passed through the filter media of nine makes of surgical masks used by dentists for protection from occupational infection. These findings lend support to the hypothesis of an airborne route for the hepatitis B infections reported for dental professionals.