Secondary flow driven by Lorentz forces in a magnetohydrodynamic channel was measured in experiments conducted at the Stanford M-2 MHD facility. The channel was connected in the Hall configuration, with net Hall current controlled by means of an external power supply. Velocity measurements were made using laser Doppler anemometry. The results demonstrate that Lorentz forces generate a significant degree of secondary flow. As expected on the basis of a first order analysis, the secondary flow field was characterized by large scale vortical structures. The presence of this phenomenon may have important implications for the performance of MHD generators.