Vertical electrolysers with a narrow cell gap between a gas-evolving electrode and a membrane or diaphragm are used to produce industrial gases. Generally, the local current density decreases with height in the cell. Electrolyses are carried out with a KOH solution in a tall vertical divided rectangular cell with two gas-evolving electrodes. Either the hydrogen or the oxygen bubbles containing solution from the divided cell are passed through a small measuring cell. Ohmic resistance experiments are carried out in the small measuring cell with a gas-evolving electrode and a gas diffusion electrode, on which no gas bubbles are evolved. The effect of various parameters, viz. current density, solution flow rate and temperature, on the ohmic resistance of solution in the measuring cell are determined. It is found that the normalized ohmic resistance of the solution in the measuring cell during electrolysis increases with current density and with the gas voidage in the bulk of solution, decreases with increasing solution flow rate and is practically independent of temperature at 25 to 60 OC. Moreover, it is found that for an oxygen evolving electrode in a solution containing only oxygen bubbles, as well as for a hydrogen evolving electrode in a solution containing only hydrogen bubbles, the normalized resistance of the solution between the gas-evolving electrode and the nongas evolving electrode is given by a relatively simple empirical relation. A relation is derived describing the gas voidage in the solution as a function of the distance from the gas-evolving electrode in the presence and the absence of gas bubbles in the bulk solution.