The influence of a steady, homogeneous magnetic field on the slip ratio in a liquid metal bubbly flow is investigated. A one-dimensional model has been developed describing the motion of a multitude of bubbles in a magnetohydrodynamic flow. Calculations are presented for magnetic fields directed transverse or parallel to the mean flow direction. While in the longitudinal case the slip decreases monotonously with the growing magnetic field, it also decreases initially, passes a minimum and increases again if (B) over right arrow is directed transverse to the flow. In order to validate the theoretical predictions, experiments are performed in liquid metal flows exposed to a transverse or a longitudinal magnetic field.