  We calculate analytically asymptotic values of quasi-normal frequencies of
four-dimensional Kerr black holes by solving the Teukolsky wave equation. We
obtain an expression for arbitrary spin of the wave in agreement with Hod's
proposal which is based on Bohr's correspondence principle. However, the range
of frequencies is bounded from above by $1/a$, where $a$ is the angular
momentum per unit mass of the black hole. Our argument is only valid in the
small-$a$ limit which includes the Schwarzschild case.
