Differences and analogies between disorder-induced localization and electric-field-induced localization are discussed. Calculations using a tight binding model and transfer matrix method for disordered superlattices are reported. Our results indicate the existence of residual structures in the energy spectrum of the disordered superlattices, which are absent in the Stark localization case. The residual structure in the Anderson localization case can be interpreted as arising from the presence of the neighboring of quantum wells with the same width and energy levels. (C) 1998 Academic Press Limited.