Abstract: There is disclosed apparatus for selectively electrolytically treating defined regions of a continuously moving conductive workpiece. The apparatus comprises means for conveying the workpiece through an electrolytic treatment zone of the apparatus where it is contacted with a treatment electrolyte; the conveying means affording masking means to mask the workpiece so that electrolyte contacts only the defined regions; the conveying means comprising an endless chain affording indexing means by which the workpiece is located in register with the masking means; means for supplying electrolyte to the masked workpiece; and means for passing a current between the workpiece as one electrode and another electrode; the means for conveying the workpiece comprising two endless chain conveyors made of articulated links of electrically non-conductive material between which the workpiece is held whilst it is passed through the treatment zone.