NOVELTY - A method for the production of membranes coated with catalyst on both sides for use in electrochemical devices, involves coating two supports separately with an ionomer layer and a catalyst layer (anode and cathode respectively), removing the supports and bonding the two ionomer layers together.    USE - For the production of membrane-electrode units for use in fuel cells.    ADVANTAGE - A simple and cost-effective method for the production of membranes coated on both sides with catalyst and membrane-electrode units for electrochemical devices, especially by continuous production (roll-to-roll). The method also prevents the membrane from swelling when the liquid catalyst solution is applied.    DETAILED DESCRIPTION - A method for the production of membranes coated with catalyst on both sides, for use in electrochemical devices, involves (A) making a first semi-finished product (SFP1) by coating an ionomer layer onto a support, applying an anode catalyst layer by using a catalyst ink and then drying the anode catalyst, (B) making a second semi-finished product (SFP2) by coating a second ionomer layer onto a second support, applying a cathode catalyst layer by using a second catalyst ink and then drying the cathode catalyst, and (C) removing the first and second supports and then combining the two SFPs by bonding the two ionomer layers together. INDEPENDENT CLAIMS are included for    (1) a method for the production of a membrane-electrode unit for electrochemical devices, by making a catalyst layer from a first ionomer etc. as above, removing the support, optionally applying a second ionomer layer to a gas diffusion electrode and then bonding the first ionomer layer to the gas diffusion electrode    (2) catalyst-coated membranes (11, 23) as above, comprising two semi-finished products (2, 7; 24, 25) bonded together, with SFP1 (2, 24) comprising an ionomer layer (4, 26) attached to an anode catalyst layer (5, 28) and SFP2 (7, 25) comprising a second ionomer layer (9, 27) attached to a cathode catalyst layer (10, 29), and having a frame (31) with a projecting edge of an SFP (30), an intermediate membrane (40), an ionomer layer (42) or a membrane (45), or which is arranged as an intermediate frame (48) between two ionomer layer edges (43, 44)    (3) fuel cells containing at least one membrane as described above    .