Fuel cell stack in which anodes and cathodes, and preferably also the membrane separating these, are made of relatively brittle material. To prevent the risk of breakage, and thus leaks, these are enclosed with a tight fit in a pressure vessel and mechanical pressure is produced on raising the temperature. The pressure vessel is preferably of elongated construction and a number of fuel cells are arranged alongside one another. The opposite ends of the pressure vessel delimit compartments for the supply and removal of one of the reactants. The other reactant is supplied to the pressure vessel and removed therefrom close to the ends of the fuel cells.