The Hall effect in the magnetohydrodynamic (MHD) channel flow of a plasma leads to the presence of transverse Lorentz forces. The non uniform distribution of these body forces may cause secondary flows to develop; these can exert a significant influence on the plasma momentum, thermal and electrical behaviour. The effect is predicted to be large for envisioned large-scale MHD devices. An experimental study of this phenomenon is described. The apparatus consisted of a laboratory-scale MHD channel in which a controlled net axial current was applied. Plasma velocities were measured using laser-Doppler anemometry. The results demonstrate that transverse Lorentz forces can drive intense secondary flows at a value of the magnetic interaction parameter based on the Hall current of approximately one. The peak measured transverse velocities were 15 % of the bulk velocity. Qualitatively, the basic character of the large-scale secondary flow structure was in accord with a simple model based on a first-order distribution of the axial current density. Measurements were also made under a variety of conditions of the profiles of mean axial velocity and of the axial and transverse components of turbulence intensity, of electrode surface temperatures and of plasma voltage distributions. These results all support the conclusion that convective transport by MHD secondary flow caused significant asymmetries to develop in the cross-plane distribution of scalar quantities.