The frequency response of the limiting current to a sinusoidal speed modulation at a rotating hemispherical electrode (RHSE) was calculated by using a series development of the colatitude θ with ten terms. The unsteady hydrodynamic problem was solved first and then the unsteady mass transport problem was considered. The theoretical expressions were experimentally confirmed in potentiostatic regulation at limiting current over a wide frequency range for the reduction of to in 2 M NaOH solution, with a nickel RHSE.