Magnetic forces can adversely affect weighings since, without systematic investigation, these spurious forces cannot be distinguished from the gravitational forces to be compared in the determination of mass. Magnetic forces can result from the mutual interaction of two mass standards as well as between a mass standard and the mass comparator being used for the weighing. Magnetic forces arise in the influence of a magnetic field gradient on a mass standard possessing a magnetic dipole moment; the latter may either exist permanently or may be induced by the applied magnetic field. This report summarises the effects of magnetism in weighing and methods developed to determine the magnetic properties of mass standard and comparator.