Abstract: A system for treating materials using microwave radiation comprising a generally pentagonal casing supporting at least one microwave source centrally of each side of the casing, a central cylindrical passageway for conveying the material to be treated and towards which the microwave sources are directed, the corners of the pentagonal casing acting as reflectors which reflect any microwave radiation passing through the material being treated back towards the material. Means may be provided for preheating material to be treated using heat collected from the treated material and from each of the microwave sources. The material to be treated may be fed by gravity through the central passageway or the passageway may be disposed horizontally and the material fed through the passageway using an auger or a conveyor belt. The conveyor belt is most conveniently supported by inclined rollers so that the material being conveyed adopts a profile which is at least partially cylindrical in shape.