  A simple numerical method to study the effect of an applied magnetic field on
the energy spectrum of non-periodic superlattice structures is presented. The
magnetic field could be either parallel or perpendicular to the growth
direction. Our method is based on the transfer matrix technique and on the
effective mass approximation. We discuss the advantages and disadvantages of
the proposed approach using several examples. In particular, we study the
perturbation to the energy spectrum of periodic superlattice induced by the
introduction of an enlarged well. We found that these perturbations are
negligible for B//z but relevant for B$\perp $z. Preliminary results for
Fibonacci superlattices in magnetic fields are presented as well. In these
quasi-periodic structures the energy levels become strongly dispersive in
presence of a perpendicular magnetic field.
