OBJECTIVE To investigate the efficacy of preoxygenation by eight deep breaths in 60 seconds with the Mapleson A (Magill) system, the circle anesthesia system, or the Mapleson D system at an oxygen flow of 5 L/min or 10 L/min. METHODS Randomized, clinical study. METHODS Operating room of a university hospital. METHODS 10 healthy volunteers. METHODS Volunteers underwent 6 preoxygenation trials consisting of 8 deep breaths in 60 seconds using the Mapleson A, Mapleson D, and the circle anesthesia systems at an oxygen flow of 5 L/min and 10 L/min. METHODS Fractional end-tidal oxygen concentration (F(ET)O(2)) was measured at 15-second intervals during preoxygenation. RESULTS At an oxygen flow of 10 L/min, mean F(ET)O(2) values at 60 seconds of preoxygenation were comparable among the Mapleson A, Mapleson D, and the circle anesthesia systems (87 +/- 2.1%, 87 +/- 1.6%, 87 +/- 1.6%, respectively). Using an oxygen flow of 5 L/min, mean F(ET)O(2) values at 60 seconds were similar among the Mapleson A, Mapleson D, and circle anesthesia systems (74 +/- 4.1%, 75 +/- 2.6%, 74 +/- 4.4%, respectively); however, they were significantly lower than the corresponding values achieved at an oxygen flow of 10 L/min. CONCLUSIONS The 8-deep-breaths in 60 seconds technique at an oxygen flow of 10 L/min can achieve adequate preoxygenation with the Mapleson A (Magill), Mapleson D, and circle anesthesia systems. Suboptimal preoxygenation is obtained with the three systems when the oxygen flow used is 5 L/min.