NOVELTY - The membrane electrode unit for use in fuel cells, comprises two electro-chemically active electrodes separated by a polymer electrolyte membrane, which has reinforcement elements and which is fiber-reinforced. The reinforcement elements partly penetrate the electrolyte membrane, comprise glass fibers, mineral fibers, natural fibers, carbon fibers, boron fibers, synthetic fibers, polymer fibers and/or ceramic fibers and have a maximum diameter of 10-500 microns, Young's modulus of 5 GPa and an elongation at rupture of 0.5-100 %.    USE - Membrane electrode unit for use in fuel cells (claimed).    ADVANTAGE - The membrane electrode unit can be produced simply and economically and can be reproducible and ensures long service life of the fuel cells as well as enables to use in high operating temperature.    DETAILED DESCRIPTION - The membrane electrode unit for use in fuel cells, comprises two electro-chemically active electrodes separated by a polymer electrolyte membrane, which has reinforcement elements and which is fiber-reinforced. The reinforcement elements partly penetrate the electrolyte membrane, comprise glass fibers, mineral fibers, natural fibers, carbon fibers, boron fibers, synthetic fibers, polymer fibers and/or ceramic fibers and have a maximum diameter of 10-500 microns, Young's modulus of 5 GPa and an elongation at rupture of 0.5-100 %. The reinforcement elements have 5-95 volume % related to total volume of the electrolyte membrane. The reinforcement elements receive a strength that differs in the force stretch diagram with 20degreesC of the reference strength of the electrolyte membrane with reinforcement elements, compared with the polymer electrolyte membrane without reinforcement elements, in the range of 0-1 % elongation in a place around 10 %. The acid content is 3-50 mol per repeating unit polymers. INDEPENDENT CLAIMS are included for:    (1) a procedure for the production of a membrane electrode unit; and    (2) a gas cell having diaphragm electrode unit.