  Assuming atmospheric neutrino oscillations with dominant nu_mu<--->nu_tau
transitions, we discuss how subdominant nu_e mixing (within the Chooz reactor
bounds) can alter the zenith distributions of neutrino-induced electrons and
muons. We isolate two peculiar distortion effects, one mainly related to nu_e
mixing in vacuum and the other to matter oscillations, that may be sufficiently
large to be detected by the SuperKamiokande atmospheric nu experiment. These
effects (absent for pure two-flavor nu_mu<--->nu_tau transitions) do not vanish
in the limit of energy-averaged oscillations.
