We study the resonant tunnelling in double-barrier heterostructures via Landau levels in the sequential tunnelling approach. The effects of the space-charge formation in the electrodes and in the well together with inelastic-scattering broadening are taken into account. Under appropriate approximations, the tunnelling current and differential conductance can be written as simpler forms which analytically reproduce the main features of experiments. Then the dependences on the temperature and magnetic field are studied numerically; these are also in accordance with experiments. Copyright © 1994 IOP Publishing Ltd.