  We consider the Blandford-Znajek process of electromagnetic extraction of
energy from a general axially symmetric asymptotically flat slowly rotating
black hole. Using the general parametrization of the black-hole spacetime we
construct formulas for the flux of the magnetic field and the rate of energy
extraction, which are valid not only for the Kerr spacetime, but also for its
arbitrary axially symmetric deformations. We show that in the dominant order
these quantities depend only on a single deformation parameter, which relates
the spin frequency of a black hole with its rotation parameter.
