Centrifugal acceleration of charged test particles at the base of a rotating jet magnetosphere is considered. Based on an analysis of forces we derive the equation for the radial accelerated motion and present an analytical solution. It is shown that for particles moving outwards along rotating magnetic field lines, the energy gain is in particular limited by the breakdown of the bead-on-the-wire approximation which occurs in the vicinity of the light cylinderrL.The corresponding upper limit for the maximum Lorentz factor&ggr;maxfor electrons scales∝B2/3rL2/3,withBthe magnetic field strength atrL,and is at most of the order of a102–103for the conditions regarded to be typical for BL Lac objects. Such values suggest that this mechanism may provide pre-accelerated seed particles which are required for efficient Fermi-type particle acceleration at larger scales in radio jets. ©2001 American Institute of Physics.