Oxyhydrogen detonations at 1 atm, covering a wide range of compositions, have been made to interact with a 0.62 Wb/m 2 magnetic field in an orthogonal field-flow-electrode configuration under open-circuit conditions. It is shown that the measured open-circuit voltage can be used to estimate the flow conditions in and behind the detonation. Several electrode systems have been examined, including strip and point electrodes flush with the wall of the detonation tube, and point electrodes immersed in the flow, with varying probe gap. The results indicate that a considerable velocity gradient exists across the tube, and, in consequence, allowance must be made for the effect of cool boundary layers in all probe experiments under similar conditions. Measurements of the flow velocity of the core of gas in the center of the tube support the predictions of the Zeldovich-Döring-Von Neumann theory.