The frequency response or the limiting current to a sinusoidal speed modulation at a rotating hemispherical electrode (RHSE) was calculated by using a series development of the colatitude theta 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 (10(-2) < p < 2) for the reduction of Fe(CN63- to Fe(CN)(6)(4-) 2 M NaOH solution, with a nickel RHSE. (C) 2000 The Electrochemical Society. All rights reserved.