The process of the penetration of hydrogen through metal membranes under potentiostatic conditions taking into account the migration of the discharging ions in the diffusion layer was considered theoretically. The quantitative relationships obtained have been confirmed experimentally. It is shown that the magnitude of the hydrogen penetration current depends essentially on the rate of arrival of hydroxonium ions at the cathodic side of the membrane due to diffusional, convective, or migrational transfer and, therefore, on the composition of the solution. 5 refs.