  The flux of muons induced by atmospheric neutrinos has been measured with the
MACRO detector. Different event topologies have been detected, due to neutrino
interactions in the apparatus and in the rock below it. The upward-throughgoing
muon sample is the larger one and is generated by neutrinos with a peak energy
of ~100 GeV. The observed upward-throughgoing muons are 26 % fewer than
expected and the zenith angle distribution does not fit with the expected one.
Assuming \mutau neutrino oscillation, the angular shape and the normalization
factor suggest maximal mixing and \Delta m^2 of a few times 10^{-3} eV^2. Also
the other event categories induced by low-energy neutrinos (peak energy ~ 4
GeV) show a deficit of observed events. The value of this deficit and its
uniformity with respect to the angular bins are in agreement with the
oscillation parameters suggested by the analysis of the upward-throughgoing
muon sample.
