Abstract: Arrangement for working internal rotational surfaces of metal parts in a cylindrical cavity in a blind bore or in a throughgoing opening having a high slenderness ratio. For working, the arrangement uses an electrode connected to the negative pole of a source of burning electrical impulses, the positive pole of such source being conductively connected with the worked metal part. The electrode is fixed conductively on a supporting tube which is arranged rotatably and eccentrically in a cylindrical hollow space from which it is insulated. In the course of the working operation the electrode or the workpiece rotates, and the electrode performs an axial advance relative to the workpiece.