Abstract: The invention relates to a process of treating workpieces consisting of hides, skins, pieces of leather or the like and is characterized by subjecting the workpiece in conjunction with a drying operation to lateral and longitudinal stretching by way of a stretching operation which comprises extension of an elastic conveyor belt on which the workpiece is conveyed. The invention also relates to machine units which can be assembled to form complete treating plants and each of which is equipped with an elastic conveyor belt for conveyance of the workpiece and with apparatus for providing, by extension and bending of the conveyor belt, a stretching and softening treatment of the workpiece, and preferably also with apparatus for drying or remoistening the workpiece.