Abstract
The dynamical exponent z for the critical relaxation of spin systems in quenched random fields has been calculated in three-loop order. For both Heisenberg and Ising systems the result is z=2+2 eta , where the static exponent eta has its usual meaning. It is suggested that this result may be exact to all orders, leading to unusually slow relaxation, with z=4, at the lower critical dimension of the random-field Ising model.