General expressions for the acoustoelectric current in the presence of external electric and magnetic fields have been derived. The Weinreich relation is shown to be valid in materials in which carriers of one sign only are present, to the extent that collision‐drag effects may be neglected. The Weinreich relation is not valid for semimetals. However, in high magnetic fields, the acoustoelectric current and field in semimetals are proportional to the attenuation. The acoustoelectric field is then in the directionq×H, whereqis the wave vector, andHthe magnetic field. The acoustoelectric current reinforces the original direct current under amplifying conditions, in agreement with observations of anomalous magnetoresistance in Bi.