A multichannel biopotential amplifier for simultaneous use with biomagnetic measurements in a magnetically shielded room is designed and evaluated. Particular care is taken to make the amplifier electromagnetically compatible with the biomagnetic instruments over the whole frequency spectrum, from DC to RF. The electromagnetically quiet environment allows the use of high electrode impedances; the preamplifier has been designed accordingly. Special care is taken to analyse the coupling mechanisms of mains interference to the amplifier. Over 170 simultaneous electric and magnetic recordings have been performed using the system in a hospital environment.