Abstract: The invention relates to an electrolyzer for the electrolysis of water in hydrogen and oxygen with a number of electrolytic cells, each containing an anode and a cathode, connected in series in a cell block surrounded by a pressure vessel. At one end of the cell block is a first electrode, and at the opposite end of the cell block is a second electrode. Both are connected with leading-in cables, which run through the pressure vessel and conduct the electric current to the cell block, the interior of the pressure vessel being filled with pressurized water surrounding the cell block. In accordance with the invention, it is envisaged that the first electrode is placed inside the cell block so as to be electrically isolated, by encapsulation, with respect to the pressurized water, and that there is a channel, sealed against the pressurized water, that leads from the cell block through the pressurized vessel to the outside.