  We investigate here the particle acceleration by Kerr naked singularities. We
consider a collision between particles dropped in from infinity at rest, which
follow geodesic motion in the equatorial plane, with their angular momenta in
an appropriate finite range of values. When an event horizon is absent, an
initially infalling particle turns back as an outgoing particle, when it has
the angular momentum in an appropriate range of values, which then collides
with infalling particles. When the collision takes place close to what would
have been the event horizon in the extremal case, the center of mass energy of
collision is arbitrarily large, depending on how close is the overspinning Kerr
geometry to the extremal case. Thus the fast rotating Kerr configurations if
they exist in nature could provide an excellent cosmic laboratory to probe
ultra-high-energy physics.
