The nature of the metal–insulator transition in the doped manganates is not well understood. The difficulty in understanding the transition stems from the variety of physical phenomena that seem to be of importance. The manganates have both magnetic as well as structural transitions that correlate with the metal–insulator transition. In an effort to clarify the situation a model based on temperature (T) and field-dependent (H) mobility edges induced by quasistatic magnetic disorder is proposed. The dependence of the mobility edge on field and temperature is derived using the localization function technique. This technique essentially examines the quantum diffusion of a localized particle as a function of time. The mobility edges are shown to move through the Fermi level if the Fermi energy sits at the edge of a band as suggested by photoemission experiments. Additionally, the formation of polarons is enhanced in the vicinity of a mobility edge since the electronic wave functions are nearly fractal in character and further localized by lattice distortions. These lattice distortions can be considered as parasitic on the localization induced by the quasistatic spin disorder and have the same temperature dependence as the magnetic transition. © 1997 American Institute of Physics.