The present invention relates to treatment units for the wet-chemical or electrolytic treatment of flat workpieces 1, such as metal foils, printed circuit foils or printed circuit boards, in which the workpieces are transported on a conveying path by means of conveying members 6. The treatment unit comprises carrier elements with recesses , said carrier elements being oriented to be parallel to the conveying path, and at least one module system for carrying the conveying members that consist of insertion elements 14, 26, preferably arranged in pairs, the at least one module system being configured such that it registers with and is preferably slidable into the recesses of the carrier elements. The treatment unit is preferably utilized in horizontal conveyorized lines.