Study Objective To determine the blood propofol concentration of anesthesiologists who were exposed to the expired gases of patients receiving propofol-based intravenous (IV) sedation. Design Prospective controlled investigation and laboratory analysis. Setting Operating room of a university hospital and an independent technical laboratory. Subjects 5 anesthesiologists who independently delivered propofol-based IV sedation to patients presenting for first trimester termination of pregnancy. In addition, a patient receiving propofol-based IV sedation was recruited as a positive control. A laboratory technician who never had previous exposure to propofol was recruited as a negative control. Interventions Blood samples were obtained from each anesthesiologist before and after an 8-hour work period of anesthesia care of patients as described above. Blood samples were also obtained from the positive control, following propofol-based IV sedation, and the negative control. Measurements An independent laboratory determined the blood propofol concentrations using a gas-liquid partition chromatograph and verified the results by repeated measurements in order to avoid a laboratory error. The gas-liquid partition chromatograph had an analytic capability that set the detection limit for propofol at 50 ng/mL. Main Results None of the anesthesiologists had detectable blood propofol concentration in either the pre-exposure or post-exposure sample. The positive control and the negative control had detectable and non-detectable blood propofol concentration, respectively. Conclusions This experiment did not detect propofol in the blood of anesthesiologists who administered propofol-based IV sedation to patients.