  Scattering of particles with different masses and energy in the gravitational
field of rotating black holes is considered as outside as inside the black
hole. Expressions for scattering energy of particles in the centre of mass
system are obtained. It is shown that scattering energy of particles in the
centre of mass system can obtain very large values not only for extremal black
holes but also for nonextremal ones if one takes into account multiple
scattering. Numerical estimates for the time needed for the particle to get
ultrarelativistic energy are given.
