Dental surgery performed with high speed instruments, such as a dental turbine, air motor, or micro-engine handpiece, produces a large amount of splattering and particles, which can be contaminated by micro-organisms from the oral cavity. It has been speculated that such particulate mists contain blood-based elements. In the present study, we investigated whether blood-contaminated aerosol was present in a room where oral surgery was performed with high speed instruments. An extra-oral evacuator system was used for sample collection (N=132). For the experiment, a non-woven towel was set on the nozzle of the evacuator as a filter and invisible mist was collected at distances of 20, 60 and 100cm from the surgical site. A leucomalachite green presumptive test was performed with each filter after every tooth extraction. At locations 20 and 100cm from the surgical site, 76% and 57%, respectively, of the particulates were positive in blood presumptive tests. Based on our results, we consider that blood-contaminated materials have the potential to be suspended in air as blood-contaminated aerosol. These results indicate the risk of cross-infection at the dental practice for immunocompromised patients as well as healthy personnel.